CAIRO -- Egypt's new president moved to assert his authority Saturday by naming a chief rival of ousted leader Mohammed Morsi as interim prime minister and holding crisis talks with security officials on efforts to reclaim control of the streets.

The steps by the untested Adly Mansour, however, are likely to deepen the defiance by Islamist opponents who have turned parts of the Cairo into vigilante-guarded strongholds and have issued blood oaths to battle until Morsi is restored.

After a night of clashes that claimed at least 36 lives, both sides appeared to be preparing for the possibility of more violence as Egypt's political unraveling increasingly left little room for middle ground or dialogue.

In the eastern suburb of Nasr City - near the main rallying point for Morsi's Muslim Brotherhood - lines of fighters brandished homemade weapons and body armor at road blocks affixed with Morsi's picture.

Next door in the relatively upscale Heliopolis district, people chanted against Morsi and honked car horns in appreciation of roadblocks manned by Egypt's military - whose snub of Morsi's authority earlier this week tipped the scales against Egypt's first elected leader.

Mansour's decision to bring pro-reform leader and Nobel laureate Mohamed ElBaradei into the key government role of prime minister is also certain to help cement the loyalties of the anti-Morsi forces.

The president planned to swear-in ElBaradei later Saturday, said Khaled Dawoud, an official with the main opposition National Salvation Front.

ElBaradei, a former director of the U.N.'s nuclear watchdog agency, led the protests against President Hosni Mubarak during the Arab Spring uprising that ended his autocratic rule in February 2011.

The revolution also opened the way for the political rise of the Muslim Brotherhood, which was long under pressure from Mubarak's Western-backed regime. Elections last year brought Morsi to the presidency, but ElBaradei remained a voice of dissent, once saying the Brotherhood lived "in a delusion" for thinking its members could manage the country on their own.

Egypt's new president - chief justice of the country's constitutional court - is little-known in international circles. But the choice of the 71-year-old ElBaradei gives the administration and prominent global figure to make its case to Washington and other Western allies trying to reassess policies after what Morsi's backers have described as a "coup." Morsi remains under detention in an undisclosed location.

Earlier, the president held talks with the army chief and interior minister in apparent attempts to work out strategies to contain another round of violence.

Morsi's supporters have vowed to take to the streets until the toppled Islamist leader is reinstated. His opponents, meanwhile, have called for more mass rallies to defend what they call the "gains of June 30."

"The people here and in all of Egypt's squares are ready for martyrdom to restore legitimacy," said Abdullah Shehatah, a senior leader of the Freedom and Justice Party, the Brotherhood's political arm. Speaking at the main sit-in site of Morsi supporters in Cairo, he said: "This coup and all its institutions are illegal."

There were no reports of major clashes in Egypt after dawn Saturday, following a night of street battles that added to an overall death toll of at least 75 in the past week.

Later, in the northern part of Sinai peninsula, gunmen shot dead a Christian priest while he shopped for food in an outdoor market on Saturday.

It was not immediately clear if the shooting was linked to the political crisis, but there has been a backlash against Christians since just before and after Morsi's ouster. Attacks have occurred on members of the minority by Islamists in at least three provinces south of Egypt. Christians account for about 10 percent of Egypt's 90 million people. Morsi's Brotherhood and hard-line allies claim the Christians played a big part in inciting against the ousted leader.

Near the main pro-Morsi gathering in Cairo, security forces boosted their presence in a sign of possible crackdowns ahead.

But it did not deter thousands of people braving a merciless summer sun in a sit-in outside the Rabaah al-Adawaiya mosque in the Nasr City district, traditionally a Muslim Brotherhood stronghold.

They hoisted posters of Morsi. Volunteers with tanks of ice water strapped on their backs sprayed participants to cool them off.

There were smaller crowds of Morsi supporters elsewhere in Cairo, including about 2,000 outside the headquarters of the Republican Guard, where Morsi was first confined by the military before he was taken to an undisclosed Defense Ministry facility. Soldiers in full combat gear watched from behind razor wire.

Late Friday, violence erupted in central Cairo as the rival camps clashed on a bridge over the Nile River. Gunfire crackled in the streets and flames leaped from a burning car. The chaotic scenes ended only after the army rushed in with armored vehicles to separate the feuding groups.

The clashes had intensified after the supreme leader of the Muslim Brotherhood, Mohammed Badie, defiantly proclaimed his followers would not give up street action until the toppled president's return to office.

"God make Morsi victorious and bring him back to the palace," Brotherhood chief Mohammed Badie proclaimed Friday before cheering supporters at a Cairo mosque in his first appearance since the overthrow. "We are his soldiers we defend him with our lives."

Hours later, his deputy, Khairat el-Shater, considered the most powerful figure in the organization, was arrested in a Cairo apartment along with his brother on allegations of inciting violence, Interior Ministry spokesman Hani Abdel-Latif told The Associated Press. Two senior leaders of the Brotherhood were released from detention on Friday pending the completion of an investigation into their alleged role in inciting violence.

Mohammed Sultan, deputy head of the national ambulance service, said at least 36 people were killed in Friday's clashes, the highest death toll in one day since the protests began last Sunday. Another 1,076 were injured.

In his first public appearance since he was sworn in, Mansour was photographed at the Muslim Friday prayers, which he performed at a mosque near his house in a suburb west of Cairo.

"I want everyone to pray for me. Your prayers are what I need from you," he told worshippers who approached him to shake his hand and wish him well, according to the independent daily el-Tahrir.

The paper said the president spoke to its reporter in a brief interview after the prayer. The president's office could not be immediately reached to confirm the comments.

"We all need national reconciliation and we will work to realize it," the newspaper quoted him as saying. "Egypt is for everyone."

On Saturday, a Cairo court adjourned to Aug. 17 the retrial of former President Hosni Mubarak over charges of corruption and involvement in the killing of protesters during the 2011 uprising that ousted him.

Mubarak and his two sons, Alaa and Gamal, who are on trial for corruption, appeared at the court session.

___

Associated Press writers Paul Schemm and Mariam Rizk contributed to this report.

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  • An opponent of Egypt's Islamist President Mohammed Morsi shouts slogans during a protest in Tahrir Square in Cairo, Egypt, Wednesday, July 3, 2013. A Defense Ministry official said army chief Gen. Abdel-Fattah el-Sissi is meeting with his top commanders, hours before the military's deadline to the president and opposition to resolve the nation's political crisis is set to expire. Arabic read " leave." (AP Photo/Amr Nabil)

  • Opponents of Egypt's Islamist President Mohammed Morsi slaughter lambs as symbols of Morsi and Muslim Brotherhood leaders during a protest in Tahrir Square in Cairo, Egypt, Wednesday, July 3, 2013. (AP Photo/Amr Nabil)

  • Opponents of Egypt's Islamist President Mohammed Morsi hold Arabic signs reading "leave," as fire rages at the Muslim Brotherhood headquarters in Alexandria, Friday, June 28, 2013. (AP Photo/Heba Khamis)

  • An opponent of Egypt's Islamist President Mohammed Morsi chants slogans during a protest outside the presidential palace, in Cairo, Egypt, Wednesday, July 3, 2013. The deadline on the military's ultimatum to President Mohammed Morsi has expired, with 48 hours passing since the time it was issued. Giant cheering crowds of Morsi's opponents have been gathered in Cairo's Tahrir Square and other locations nationwide, waving flags furiously in expection that the military will act to remove the Islamist president after the deadline ends. (AP Photo/Khalil Hamra)

  • An opponent of Egypt's Islamist President Mohammed Morsi chants slogans during a protest outside the presidential palace, in Cairo, Egypt, Wednesday, July 3, 2013. The deadline on the military's ultimatum to President Mohammed Morsi has expired, with 48 hours passing since the time it was issued. Giant cheering crowds of Morsi's opponents have been gathered in Cairo's Tahrir Square and other locations nationwide, waving flags furiously in expection that the military will act to remove the Islamist president after the deadline ends. (AP Photo/Khalil Hamra)

  • Egyptian protesters calling for the ouster of President Mohamed Morsi react as they watch his speech on a screen in a street leading to presidential palace early in Cairo on July 3, 2013. Morsi told Egyptians that he had been freely elected little more than a year ago and that he intended to continue to carry out his duties despite mass protests demanding his resignation. (MAHMUD KHALED/AFP/Getty Images)

  • Hundreds of Egyptian protesters begin to gather in Tahrir Square as the deadline given by the military to Egyptian President Mohammed Morsi approaches on July 3, 2013 in Cairo, Egypt. The president gave a defiant speech last night and vowed to stay in power despite the military threats. As unrest spreads throughout the country, at least 23 people were killed in Cairo on Tuesday and over 200 others were injured. (Photo by Spencer Platt/Getty Images)

  • Holding a picture of the second President of Egypt Gamal Abdel Nasser Hussein, hundreds of Egyptian protesters begin to gather in Tahrir Square as the deadline given by the military to Egyptian President Mohammed Morsi approaches on July 3, 2013 in Cairo, Egypt. The president gave a defiant speech last night and vowed to stay in power despite the military threats. As unrest spreads throughout the country, at least 23 people were killed in Cairo on Tuesday and over 200 others were injured. (Photo by Spencer Platt/Getty Images)

  • Thousands of Egyptian protesters begin to gather in Tahrir Square as the deadline given by the military to Egyptian President Mohammed Morsi approaches on July 3, 2013 in Cairo, Egypt. The president gave a defiant speech last night and vowed to stay in power despite the military threats. As unrest spreads throughout the country, at least 23 people were killed in Cairo on Tuesday and over 200 others were injured. It has been reported that the military has taken over state television. (Photo by Spencer Platt/Getty Images)

  • Thousands of Egyptian protesters begin to gather in Tahrir Square as the deadline given by the military to Egyptian President Mohammed Morsi approaches on July 3, 2013 in Cairo, Egypt. The president gave a defiant speech last night and vowed to stay in power despite the military threats. As unrest spreads throughout the country, at least 23 people were killed in Cairo on Tuesday and over 200 others were injured. It has been reported that the military has taken over state television. (Photo by Spencer Platt/Getty Images)

  • Thousands of Egyptian protesters begin to gather in Tahrir Square as the deadline given by the military to Egyptian President Mohammed Morsi approaches on July 3, 2013 in Cairo, Egypt. The president gave a defiant speech last night and vowed to stay in power despite the military threats. As unrest spreads throughout the country, at least 23 people were killed in Cairo on Tuesday and over 200 others were injured. It has been reported that the military has taken over state television. (Photo by Spencer Platt/Getty Images)

  • Egyptian protesters calling for the ouster of President Mohamed Morsi gather in Cairo's landmark Tahrir Square on July 2, 2013 as laser lights (L) directed at the government building spell 'Game Over.' (KHALED DESOUKI/AFP/Getty Images)

  • Opposition protesters shout slogans as they gather in thousands at qoubba Presidential Palace to protest against Egyptian President Mohammed Morsi and the Muslim Brotherhood on July 2, 2013 in Cairo. Egypt's political crisis deepened as Islamist President Mohamed Morsi snubbed an army ultimatum threatening to intervene if he did not meet the demands of the people, and five ministers led a spate of government resignations. (GIANLUIGI GUERCIA/AFP/Getty Images)

  • Egyptian supporters of President Mohamed Morsi gather in Rabaa el-Aadawia district of cairo on July 2, 2013, as opponents of Egypt's president also poured onto the streets of Cairo to press their demand that he step down after the Islamist president snubbed an ultimatum from the army to agree to the 'people's demands' or face an imposed solution. (KHALED KAMEL/AFP/Getty Images)

  • Egyptian opposition protester shout slogans as tens of thousands gather outside the Presidential Palace calling for the ouster of Egyptian President Mohammed Morsi on July 2, 2013 in Cairo. Opponents of Egypt's Mohamed Morsi poured onto the streets of Cairo to press their demand that he step down after the Islamist president snubbed an ultimatum from the army to agree to the 'people's demands' or face an imposed solution. (GIANLUIGI GUERCIA/AFP/Getty Images)

  • Egyptian protesters calling for the ouster of President Mohamed Morsi gather in Cairo's landmark Tahrir Square on July 2, 2013. Opponents of Egypt's Mohamed Morsi poured onto the streets of Cairo to press their demand that he step down after the Islamist president snubbed an ultimatum from the army to agree to the 'people's demands' or face an imposed solution. (KHALED DESOUKI/AFP/Getty Images)

  • An Egyptian opposition protester holds up the head of a sheep as tens of thousands gather outside the Presidential Palace calling for the ouster of Egyptian President Mohammed Morsi on July 2, 2013 in Cairo. Opponents of Egypt's Mohamed Morsi poured onto the streets of Cairo to press their demand that he step down after the Islamist president snubbed an ultimatum from the army to agree to the 'people's demands' or face an imposed solution. (GIANLUIGI GUERCIA/AFP/Getty Images)

  • An Egyptian youth with his face painted in the colours of the national flag look over as opponents of Egyptian President Mohamed Morsi protest calling for his ouster at Cairo's landmark Tahrir Square, on July 2, 2013. Egypt's political crisis deepened as Islamist President Mohamed Morsi snubbed an army ultimatum threatening to intervene if he did not meet the demands of the people, and five ministers led a spate of government resignations. (KHALED DESOUKI/AFP/Getty Images)

  • An Egyptian opposition demonstrator sits at the top of a column watching a military helicopter fly by, as protesters (unseen) call for the ouster of President Mohamed Morsi outside the presidential palace in Cairo, on July 2, 2013. Egypt's political crisis deepened as Islamist President Morsi snubbed an army ultimatum threatening to intervene if he did not meet the demands of the people, and five ministers led a spate of government resignations. (MAHMUD KHALED/AFP/Getty Images)

  • An Egyptian boy waves a national flag during a protest against Islamist President Mohammed Morsi in Tahrir Square in Cairo, Egypt, Tuesday, July 2, 2013. With a military deadline for intervention ticking down, protesters seeking the ouster of Egypt's Islamist president sought Tuesday to push the embattled leader further toward the edge with another massive display of people power. (AP Photo/Amr Nabil)

  • Opponent of Egypt's Islamist President Mohammed Morsi hold a large Egyptian national flag during a protest outside the presidential palace, in Cairo, Egypt, Tuesday, July 2, 2013. Egypt was on edge Tuesday following a "last-chance" ultimatum the military issued to Mohammed Morsi, giving the president and the opposition 48 hours to resolve the crisis in the country or have the army step in with its own plan. (AP Photo/Hassan Ammar)

  • Opponents of Egypt's Islamist President Mohammed Morsi wave national flags during a protest outside the presidential palace, in Cairo, Egypt, Tuesday, July 2, 2013. Egypt was on edge Tuesday following a "last-chance" ultimatum the military issued to Mohammed Morsi, giving the president and the opposition 48 hours to resolve the crisis in the country or have the army step in with its own plan. (AP Photo/Khalil Hamra)

  • An Egyptian protester waves a national flag on a roof in Tahrir Square during a demonstration against Egypt's Islamist President Mohammed Morsi in Cairo, Monday, July 1, 2013. Egypt's powerful military warned on Monday it will intervene if the Islamist president doesn't "meet the people's demands," giving him and his opponents two days to reach an agreement in what it called a last chance. Hundreds of thousands of protesters massed for a second day calling on Mohammed Morsi to step down. (AP Photo/ Manu Brabo)

  • An Egyptian protester waves a national flag in Tahrir Square during a demonstration against Egypt's Islamist President Mohammed Morsi in Cairo, Monday, July 1, 2013. Egypt's powerful military warned on Monday it will intervene if the Islamist president doesn't "meet the people's demands," giving him and his opponents two days to reach an agreement in what it called a last chance. Hundreds of thousands of protesters massed for a second day calling on Mohammed Morsi to step down. (AP Photo/ Manu Brabo)

  • An Egyptian opposition demonstrator, runs down the length of a long national flag being held by protesters calling for the ouster of President Mohamed Morsi, outside the presidential palace in Cairo, on July 2, 2013. (MAHMUD KHALED/AFP/Getty Images)

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  • Opponents of Egypt's Islamist President Mohammed Morsi protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

  • An opponent of Egypt's Islamist President Mohammed Morsi blows a whistle during a protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

  • Opponents of Egypt's Islamist President Mohammed Morsi protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

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  • Egyptian protester stands on a roof near Tahrir Square during a demonstration against Egypt's Islamist President Mohammed Morsi in Tahrir Square in Cairo, Monday, July 1, 2013. (AP Photo/Manu Brabo)

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  • Opponents of Egypt's Islamist President Mohammed Morsi chant slogans during a protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

  • Opponents of Egypt's Islamist President Mohammed Morsi chant slogans during a protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

  • An opponents of Egypt's Islamist President Mohammed Morsi blows a stadium horn during a protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

  • Opponents of Egypt's Islamist President Mohammed Morsi stand on railway bars during a protest outside the presidential palace, in Cairo, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

  • Opponents of Egypt's Islamist President Mohammed Morsi chant slogans during a protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

  • An opponent of Egypt's Islamist President Mohammed Morsi holds a poster with Arabic that reads, "Tamarod, down with the Muslim Brotherhood regime, 6/30, in front of Itihadeya," during a protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Hassan Ammar)

  • Opponents of Egypt's Islamist President Mohammed Morsi wave national flags during a protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. (AP Photo/Nariman El-Mofty)

  • Opponents of Egypt's Islamist President Mohammed Morsi protest outside the presidential palace, in Cairo, Egypt, Monday, July 1, 2013. The banner at center, with Arabic writing, reads, "leave." (AP Photo/Hassan Ammar)

  • Supporters of Egypt's Islamist President Mohammed Morsi wave national flags and his posters during a rally in Nasser City, Cairo, Egypt, late Monday, July 1, 2013. (AP Photo/ Amr Nabil)

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  • Egyptian opposition protesters celebrate on July 1, 2013 in Cairo's landmark Tahrir square after Egypt's armed forces gave President Mohamed Morsi 48 hours to meet the demands of the people or it would intervene with a roadmap. (GIANLUIGI GUERCIA/AFP/Getty Images)

  • Laser lights are directed by Egyptian protestors on military helicopters flying over the presidential palace in Cairo as hundreds of thousands of Egyptian demonstrators gather at the Egyptian Presidential Palace during a protest calling for the ouster of President Mohamed Morsi on July 1, 2013 in Cairo, Egypt. (GIANLUIGI GUERCIA/AFP/Getty Images)

  • Laser lights directed by Egyptian protestors are seen on military helicopters flying over the presidential palace in Cairo as Hundreds of thousands of Egyptian demonstrators gather at the Egyptian Presidential Palace during a protest calling for the ouster of President Mohamed Morsi on July 1, 2013 in Cairo, Egypt.(GIANLUIGI GUERCIA/AFP/Getty Images)