BEIRUT — Iran's new president expressed his country's support to Syria's embattled leader Bashar Assad's regime Sunday, saying no force in the world will be able to shake their decades-old alliance.

Hasan Rouhani's comments came as Syrian troops and rebels fought some of the fiercest battles in the mountains of the coastal province of Latakia, an Assad stronghold.

Rouhani made the comments during a meeting in the Iranian capital of Tehran on Sunday with Syrian Prime Minister Wael al-Halqi, Syria's state news agency SANA said.

Syria has been Tehran's strongest ally in the Arab world since Iran's 1979 Islamic Revolution.

Iran has been one of Assad's staunchest backers since Syria's crisis began. Tehran is believed to have supplied Assad's government with billions of dollars since the country's crisis began in March 2011. Iran-supported Hezbollah also has sent fighters into Syria to bolster an offensive by Assad forces.

"The Islamic Republic of Iran aims to strengthen its relations with Syria and will stand by it in facing all challenges," SANA quoted Rouhani as saying in a report from Tehran. "The deep, strategic and historic relations between the people of Syria and Iran ... will not be shaken by any force in the world."

Rouhani was elected in June and was endorsed by the country's supreme leader on Saturday, allowing him to begin acting as president. He was sworn in Sunday.

Assad vowed Sunday evening to crush the rebels trying to overthrow him, saying Syria is between two choices: "a state of the law or a state run by thieves and bandits."

Assad spoke while taking part in an iftar, the meal that breaks the dawn-to-dusk fast during the Muslim holy month of Ramadan. The iftar was attended by government officials, religious leaders and members of the country's unions and political parties, SANA said.

It was Assad's second public appearance this week after he visited troops in the Damascus suburb of Daraya on Thursday to mark Army Day.

Assad said "terrorism cannot be dealt with politically but should be struck with an iron fist."

Assad's troops have achieved victories in the past two months mostly near the capital Damascus and in the strategic central province of Homs that links the capital Damascus with Assad's stongholds on the coast.

Assad said his army, which was built to fight a conventional war against its main enemy Israel, has been able to adapt to the guerrilla warfare it is facing.

The Syrian leader criticized Persian Gulf states that he said are demanding democracy in Syria despite human rights abuses in their own countries.

"Their political systems belong to the middle ages where there are no parliaments or elections," Assad said.

Saudi Arabia and Qatar that have been among the strongest backers of the Syrian opposition.

Rouhani condemned foreign intervention in Syria, saying that the Arab country is passing through a "failed attempt" to strike at the "axis of resistance and rejection to Zionist-American plans in the region," SANA quoted him as saying.

Damascus and Tehran reject the idea that there is an uprising in Syria and say the country is being subjected to an Israeli-American conspiracy because of its support to militant groups such as Lebanon's Hezbollah.

SANA quoted Rouhani as saying that Syria will come out of this war "victorious."

Al-Halqi said the Syrian people will "not forget friends who stood by their side during times of difficulties," SANA reported.

More than 100,000 people have been killed since the uprising against the Assad family's four-decade rule began in March 2011. The revolt later escalated into a civil war, which has uprooted millions of people from their homes.

Assad's and Rouhani's statements came as Syrian troops and rebels fought Sunday some of the fiercest battles in the mountains of the coastal province of Latakia, an Assad stronghold.

The Britain-based Syrian Observatory for Human Rights said the clashes in the Jabal al-Akrad region in Latakia province began around dawn when rebels attacked government forces' posts. It said both sides used tanks, artilleries and mortars in the fighting, while government warplanes took part in the battles.

Although much of Latakia has been under the firm control of Assad's forces, some mountainous regions such as Jabal al-Akrad and Jabal al-Turkomen have witnessed fighting because they are close to rebel-held areas.

The observatory said 12 rebels, including foreign fighters, were killed in the fighting, as well as 19 troops and pro-government gunmen. Dozens were wounded as well, it said.

The Local Coordination Committees, another activist group, said at least eight people were killed in the fighting in Latakia province. It added that rebels fired Russian-made Grad rockets at government positions.

Earlier on HuffPost:

Loading Slideshow...
  • A Syrian rebel tries on a gas mask seized from a Syrian army factory in the northwestern province of Idlib on July 18, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Syrian volunteers try to evacuate 8-year-old Mahmud Fayad still trapped under the rubble of a destroyed house after a barrel bomb was dropped from an air force helicopter in Saraqeb in northwestern Syria on July 20, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • In this photo released by the Syrian official news agency SANA, Syrian citizens gather near damaged cars that were burned after a car bomb exploded in the suburb of Jaramana, Damascus, Syria, Thursday, July 25, 2013. (AP Photo/SANA)

  • An Indian Shiite Muslim woman breaks down as she holds a placard during a protest rally organized to condemn an attack on a Shiite shrine in Syria, in Bangalore, India, Friday, July 26, 2013. (AP Photo/Aijaz Rahi)

  • A Syrian man stands amidst the rubble of the Othman mosque, in Syria's eastern town of Deir Ezzor, on July 24, 2013. (KARAM JAMAL/AFP/Getty Images)

  • An injured Syrian man receives medical treatment at a hospital in the town of Ariha, in the northwestern province of Idlib, on July 21, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • This Tuesday, July 9, 2013 citizen journalism image provided by Aleppo Media Center AMC, which has been authenticated based on its contents and other AP reporting, shows buildings are seen damaged by Syrian government airstrikes and shelling, in the Salah al-Din neighborhood of Aleppo, Syria. (AP Photo/Aleppo Media Center AMC)

  • Syrian volunteers cry of joy after rescuing 8-year-old Mahmud Fayad who was trapped under the rubble of a destroyed house after a barrel bomb was dropped from an air force helicopter in Saraqeb in northwestern Syria on July 20, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • In this photo released by the Syrian official news agency SANA, Syrian citizens gather near damaged cars that were burned after a car bomb exploded in the suburb of Jaramana, Damascus, Syria, Thursday, July 25, 2013. (AP Photo/SANA)

  • Syrians inspect the site where a barrel bomb dropped by an air force helicopter exploded in Saraqeb in northwestern Syria on July 20, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Syrian men rush a heavily wounded man to hospital in Saraqeb in northwestern Syria after a barrel bomb dropped by an air force helicopter exploded less than 10 metres away from his car on July 20, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Indian Shiite Muslim women raise slogans as they participate in a rally organized to condemn an attack on a Shiite shrine in Syria, in Bangalore, India, Friday, July 26, 2013. (AP Photo/Aijaz Rahi)

  • In this photo released by the Syrian official news agency SANA, Syrian citizens look at a damaged building after a car bomb exploded in the suburb of Jaramana, Damascus, Syria, Thursday, July 25, 2013. (AP Photo/SANA)

  • Syrians search for survivors under the rubble of a destroyed house after a barrel bomb was dropped from an air force helicopter in Saraqeb in northwestern Syria on July 20, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Doctors treat a young Syrian girl hit by shrapnel following an air raid in the northern Syrian town of Saraqeb, in the Idlib province, on July 19, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • A Syrian girl walks next to the debris of her house, after it was targeted by a missile, in the northwestern Syrian province of Idlib on July 18, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • In this Wednesday, July 3, 2013 citizen journalism image provided by Lens Young Homsi, which has been authenticated based on its contents and other AP reporting, shows Syrians inspecting the rubble of damaged buildings due to government airstrike and shelling, in the al-Hamidiyyeh neighborhood of Homs province, Syria. (AP Photo/Lens Young Homsi)

  • A picture taken on July 18, 2013 shows smoke rising from a building after opposition forces attacked a government forces held checkpoint in Syria's northeastern city of Deir Ezzor on July 18, 2013. (ABO SHUJA/AFP/Getty Images)

  • This aerial view shows the Zaatari refugee camp on Thursday, July 18, 2013 near the Jordanian city of Mafraq, some 8 kilometers (5 miles) from the Jordan-Syria border. (AP Photo/Mandel Ngan, Pool) AP10ThingsToSee

  • A rebel fighter points his gun towards pro-government forces' positions during clashes in the Salaheddine district of the northern Syrian city of Aleppo, on July 9, 2013. (JM LOPEZ/AFP/Getty Images)

  • Syrian children wait in line to collect a free Iftar meal in the northern city of Raqqa during the Muslim holy month of Ramadan on July 14, 2013. (MEZAR MATAR/AFP/Getty Images)

  • A rebel fighter aims his weapon to Syrian government forces' positions inside a destroyed school in the Izaa district of Aleppo, on July 14, 2013. (JM LOPEZ/AFP/Getty Images)

  • A rebel fighter from the Suqur Al-Sham brigades, takes a nap after his night shift in a trench along the highway that connects Idlib city with Latakia, 100m far from the Syrian regime's forces's positions, on July 14, 2013. (DANIEL LEAL OLIVAS/AFP/Getty Images)

  • In this citizen journalism image provided by Aleppo Media Center AMC, which has been authenticated based on its contents and other AP reporting, buildings are seen damaged by Syrian government airstrikes and shelling in Aleppo, Syria, Monday, July 8, 2013. (AP Photo/Aleppo Media Center AMC)

  • Family members pray over the bodies of two Syrian children, Safia Baour, 14, and her three-year-old brother Khaled, who were killed after a shell landed on their family home as they gathered to break their fast with the iftar meal on July 13, 2013 in Maaret Al-Numan in southern Idlib province. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Syrian rebels head to the town of Bsankol in the northwestern province of Idlib to join comrades fighting regime forces for the control of the highway that connects Idlib with Latakia on July 11, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • An opposition fighter stands over seven year old Ahmad Jabir, who was injured alongside some his family members by a shell, as he lies on a X-Ray machine after he brought the boy to a hospital in the town of Al-Bara, in Syria's northwestern province Idlib on July 10, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Syrian rebels gather outside a building which they blew up to target a regime sniper taking shelter inside but who managed to escape in the Salaheddine district of the northern city of Aleppo on July 10, 2013. (SALAH AL-ASHKAR/AFP/Getty Images)

  • Rebel fighters look up listening as they take positions during clashes with pro-government forces in the Salaheddine district of the northern Syrian city of Aleppo, on July 9, 2013. (JM LOPEZ/AFP/Getty Images)

  • This Tuesday, July 9, 2013 citizen journalism image provided by Aleppo Media Center AMC, which has been authenticated based on its contents and other AP reporting, shows Syrian rebels running during heavy clashes with Syrian soldiers loyal to Syrian President Bashar Assad, in the Salah al-Din neighborhood of Aleppo, Syria. (AP Photo/Aleppo Media Center AMC)

  • Rebel fighters break a wall before holding a position during clashes with pro-government forces in the Salaheddine district of the northern Syrian city of Aleppo, on July 9, 2013. (JM LOPEZ/AFP/Getty Images)

  • A rebel fighter speaks on a walkie-talkie as he holds a position in a flat during clashes with pro-government forces in the Salaheddine district of the northern Syrian city of Aleppo, on July 9, 2013. (JM LOPEZ/AFP/Getty Images)

  • Syrian rebel fighters gather around a former Syrian army tank as rebels prepare to attack positions held by the Syrian army areas in the Salaheddine neighborhood of Aleppo, on July 8, 2013. (ABO MHIO/AFP/Getty Images)

  • Opposition fighters carry one of their comrades, who died on the front-line, as they were leading an attack on positions held by the government forces in the Salaheddine neighbourhood of Aleppo on July 8, 2013. (ABO AL-NUR SADK/AFP/Getty Images)

  • An opposition fighter throws a Molotov cocktail during clashes with Syrian government forces in the Salah al-Din area of the northern city of Aleppo on July 8, 2013. (ZAID REV/AFP/Getty Images)

  • In this Tuesday, July 2, 2013 citizen journalism image provided by Aleppo Media Center AMC, which has been authenticated based on its contents and other AP reporting, homes are seen destroyed by Syrian government airstrikes and shelling in the neighborhood of Karam Tarab near Aleppo International Airport in Aleppo, Syria. (AP Photo/Aleppo Media Center AMC)