NAIROBI, Kenya -- Islamic militants who staged a deadly attack on a Kenya mall said Tuesday hostages are still alive and fighters are "still holding their ground," as Nairobi's city morgue braced for the arrival of a large number of bodies of people killed, an official said.

The Kenyan Red Cross has confirmed at least 62 people have been killed, but spokesman Abbas Gullet said it was still not known how many more may be dead inside the building.

"It is certainly known that there are more casualties," he said.

A government official told The Associated Press that the morgue was preparing for up to 60 bodies, though the official didn't know an exact count. The government official insisted on anonymity so he would not face retribution from government officials.

Kenyan forces have been battling the militants for four days and police said in a tweet: "Troops now in mop up operations in the building."

The police urged people to ignore "enemy... propaganda" and assured that the defense forces were continuing to "neutralize" the terrorist threat.

In a new Twitter feed established Tuesday after previous ones were cut off, the al-Qaida-linked rebel group al-Shabab said the attack that began Saturday was "far greater than how the Kenyans perceive it."

"There are countless number of dead bodies still scattered inside the mall, and the mujahideen are still holding their ground," the group claimed.

It added that the hostages are "still alive looking quite disconcerted but, nevertheless, alive."

A city resident whose brother is taking part in the military operation inside the mall told The Associated Press that there were many dead bodies in the mall, and a government official said city morgue employees were told to prepare for many bodies.

Both the government official and the Nairobi resident insisted their names not be used so they would not face retribution from government officials.

A U.S. Embassy vehicle, identifiable by its numbered diplomatic license plate, arrived at the morgue on Tuesday. American officials have not confirmed the deaths of any U.S. citizens in the mall attack, but it appeared possible the Americans who visited the morgue - likely security officials with an agency like the FBI - could have been seeking information about one of the bodies inside.

Al-Shabab, whose name means "The Youth" in Arabic, said the mall attack was in retribution for Kenyan forces' 2011 push into neighboring Somalia. African Union forces pushed the al-Qaida-affiliated group out of Somalia's capital in 2011.

"You could have avoided all this and lived your lives with relative safety," the group Tweeted Tuesday. "Remove your forces from our country and peace will come."

After four days, authorities now say they are involved in a final push to clear out the remaining attackers. But authorities have before referred to their operations as final. And despite the Kenyan government assurances of success, an explosion and gunfire could be heard coming from the mall at around 6:30 a.m., followed by the sustained chatter of automatic weapons for about a minute almost three hours later, according to Associated Press reporters at the scene.

More shots were heard about noontime, followed by two explosions a short time later, and a plane and helicopter circled over the mall.

Security forces carried a body out of the mall, which remained on fire, with flames and smoke visible. A Kenyan soldier wearing bomb disposal protective gear also exited the building.

While the government announced Sunday that "most" hostages had been released, a security expert with contacts inside the mall said at least 10 were still being held by a band of attackers described as "a multinational collection from all over the world."

Kenyan Foreign Minister Amina Mohamed said "two or three Americans" and "one Brit" were among those who attacked the mall.

She said in an interview with the PBS "NewsHour" program that the Americans were 18 to 19 years old, of Somali or Arab origin and lived "in Minnesota and one other place" in the U.S. The attacker from Britain was a woman who has "done this many times before," Mohamed said.

U.S. officials said they were looking into whether any Americans were involved. State Department spokeswoman Jen Psaki said Monday that the department had "no definitive evidence of the nationalities or the identities" of the attackers.

Britain's foreign office said it was aware of the foreign minister's remarks, but would not confirm if a British woman was involved.

The security expert, who insisted on anonymity to talk freely about the situation, said many hostages had been freed or escaped in the previous 24-36 hours, including some who were in hiding.

However, there were at least 30 hostages when the assault by al-Shabab militants began Saturday, he said, and "it's clear" that Kenyan security officials "haven't cleared the building fully."

Kenyan government spokesman Manoah Esipisu said the country's president would make an address to the nation later in the day but said he could give no immediate details on the operation.

Kenyan security officials on Monday evening said they had claimed the upper hand as flames and dark plumes of smoke rose above the Westgate shopping complex for more than an hour after four large explosions.

Kenya's Interior Minister Joseph Ole Lenku said the evacuation of hostages had gone "very, very well" and that Kenyan officials were "very certain" that few if any hostages were left in the building.

But with the mall cordoned off and under heavy security it was not possible to independently verify the assertions. Similar claims of a quick resolution were made by Kenyan officials on Sunday and the siege continued. Authorities have also not provided any details on how many hostages were freed or how many still remain captive.

Three attackers were killed in the fighting Monday, Kenyan authorities said, and more than 10 suspects arrested. Eleven Kenyan soldiers were wounded in the running gun battles.

Al-Shabab spokesman Sheik Ali Mohamud Rage said in an audio recording posted on a militant website that the attackers had been ordered to "take punitive action against the hostages" if force was used to try to rescue them.

A Western security official in Nairobi who insisted on not being named to share information about the rescue operation said the only reason the siege hadn't yet ended would be because hostages were still inside.

Westgate mall, a vast complex with multiple banks that have secure vaults and bulletproof glass partitions, as well as a casino, is difficult to take, the official said. "They are not made for storming," he said of the labyrinth of shops, restaurants and offices. "They're made to be unstormable."

Some 12 to 15 al-Shabab militants attacked Saturday, wielding grenades and firing on civilians inside the mall, which includes shops for such retail giants as Nike, Adidas and Bose and is popular with foreigners and wealthy Kenyans.

The militants specifically targeted non-Muslims, and at least 18 foreigners were among the dead, including six Britons, as well as citizens from France, Canada, the Netherlands, Australia, Peru, India, Ghana, South Africa and China. Nearly 200 people were wounded, including five Americans.

Fighters from an array of nations participated in the assault, according to Kenya's Chief of Defense forces Gen. Julius Karangi. "We have an idea who these people are and they are clearly a multinational collection from all over the world," he said.

The attack at the Westgate mall in Nairobi's Westlands neighborhood was the deadliest terrorist attack in Kenya since the 1998 al-Qaida truck bombing of the U.S. Embassy in Nairobi, which killed more than 200 people.

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Associated Press reporters Rodney Muhumuza, Ben Curtis, David Rising, Adam Schreck and Jacob Kushner in Nairobi, Kenya, Cassandra Vinograd in London, and Abdi Guled in Mogadishu, Somalia, contributed to this report.

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  • A plume of black smoke billows over the Westgate Mall, in Nairobi, Kenya Monday, Sept. 23, 2013. Multiple large blasts have rocked the mall where a hostage siege is in its third day. Associated Press reporters on the scene heard multiple blasts and a barrage of gunfire. Security forces have been attempting to rescue an unknown number of hostages inside the mall held by al-Qaida-linked terrorists.(AP Photo/Jonathan Kalan)

  • Armed police from the General Service Unit take cover behind a wall during a bout of gunfire, outside the Westgate Mall in Nairobi, Kenya Monday, Sept. 23, 2013. Hostages being held by al-Qaida-linked terrorists in a Nairobi mall have not been released despite an earlier statement from the military that "most" had been rescued, a person connected to the situation told The Associated Press on Monday. (AP Photo/Ben Curtis)

  • Paramedics and police officers run outside the Westgate Mall in Nairobi after heavy shooting started Monday, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff. (AP Photo/Sayyid Azim)

  • Kenya security forces are seen behind a wall outside the Westgate Mall in Nairobi, Kenya Monday morning, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff that killed at least 68 people and injured 175. (AP Photo/Jerome Delay)

  • Kenya security personnel take cover outside the Westgate Mall after shooting started inside the mall early Monday morning, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff that killed at least 68 people and injured 175. (AP Photo/Sayyid Azim)

  • Kenya security forces are seen behind a wall outside the Westgate Mall in Nairobi, Kenya Monday morning, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff that killed at least 68 people and injured 175. (AP Photo/Jerome Delay)

  • Kenya security forces are seen behind a wall outside the Westgate Mall in Nairobi, Kenya Monday morning, Sept. 23, 2013. Kenya's military launched a major operation at the upscale Nairobi mall and said it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during the standoff that killed at least 68 people and injured 175. (AP Photo/Jerome Delay)

  • Onlookers gather on a hill to observe the Westgate Mall after a bout of heavy gunfire just after dawn in Nairobi, Kenya Monday, Sept. 23, 2013. Helicopters circling overhead, Kenya's military launched a major operation Sunday night at the upscale Nairobi mall and claimed it had rescued "most" of the hostages being held captive by al-Qaida-linked militants during a standoff that killed at least 68 people and injured 175. (AP Photo/Ben Curtis)

  • Relatives wait at the Nairobi City Mortuary following the mall attack in Kenya, Sunday, Sept. 22, 2013. Kenyan authorities said Islamic extremist attackers remain inside the upscale Kenyan shopping mall, holding an unknown number of hostages, after killing at least 39 and injuring 150 during Saturday's attack. (AP Photo/Khalil Senosi)

  • Groups of onlookers gather on a road looking down over the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Multiple barrages of gunfire erupted Sunday morning from the upscale Kenyan mall where there is a hostage standoff with Islamic extremists nearly 24 hours after they attacked using grenades and assault rifles. (AP Photo/Ben Curtis)

  • A line of soldiers from the Kenya Defense Forces run in front of the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Multiple barrages of gunfire erupted Sunday morning from the upscale Kenyan mall where there is a hostage standoff with Islamic extremists nearly 24 hours after they attacked using grenades and assault rifles. (AP Photo/Ben Curtis)

  • Soldiers from the Kenya Defense Forces carry a wounded colleague, following the sound of explosions and gunfire, out of the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Associated Press journalists at the scene of a hostage standoff said a barrage of gunfire erupted from the upscale Kenyan mall Sunday morning and moments later two wounded Kenyan security forces were carried out of the mall. (AP Photo/Ben Curtis)

  • Trucks of soldiers from the Kenya Defense Forces arrive after dawn outside the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Islamic extremist gunmen lobbed grenades and fired assault rifles inside Nairobi's top mall Saturday, killing dozens and wounding over a hundred in the attack. Early Sunday morning, 12 hours after the attack began, gunmen remained holed up inside the mall with an unknown number of hostages. (AP Photo/Ben Curtis)

  • Trucks of soldiers from the Kenya Defense Forces arrive after dawn outside the Westgate Mall in Nairobi, Kenya Sunday, Sept. 22, 2013. Islamic extremist gunmen lobbed grenades and fired assault rifles inside Nairobi's top mall Saturday, killing dozens and wounding over a hundred in the attack. Early Sunday morning, 12 hours after the attack began, gunmen remained holed up inside the mall with an unknown number of hostages. (AP Photo/Ben Curtis)

  • Armed special force aim their guns at the Westgate Mall in Nairobi, Kenya on Saturday, Sept. 21 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded. A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted(AP Photo/Khalil Senosi)

  • Civilians who had been hiding inside during the gun battle manage to flee from the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013. Gunmen threw grenades and opened fire Saturday, killing at least 22 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, a Red Cross official and witnesses said. (AP Photo/Jonathan Kalan)

  • A body is seen on the floor, below right, as smoke fills the air inside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013. Gunmen threw grenades and opened fire Saturday, killing at least 22 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, a Red Cross official and witnesses said. (AP Photo/Jonathan Kalan)

  • A woman who had been hiding during the gun battle runs for cover after armed police, seen behind, enter the Westgate Mall in Nairobi, Kenya, Saturday, Sept. 21, 2013. Gunmen threw grenades and opened fire Saturday, killing at least 22 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, a Red Cross official and witnesses said. (AP Photo/Jonathan Kalan)

  • An armed police officer takes cover during a bout of gunfire outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013. Gunmen threw grenades and opened fire Saturday killing at least 22 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, a Red Cross official and witnesses said. (AP Photo/Ben Curtis)

  • People run from the Westgate Mall in Nairobi, Kenya.

    Gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded. A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted.

  • A woman who had been held hostage reacts after being released.

    Suspected terrorists engaged Kenyan security forces in a drawn out gun fight at the Westgate Mall in Nairboi.

  • Woman runs for cover.

    A woman who had been hiding during the gun battle runs for cover after armed police, seen behind, enter the Westgate Mall in Nairobi, Kenya, Saturday, Sept. 21, 2013.

  • Location of the attack.

    Graphic shows detail of shopping mall site of fatal gun attack in Nairobi, Kenya.

  • View inside the mall.

    Armed police take cover behind escalators as smoke fills the air inside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • Raw: Gunmen Attack Shopping Mall in Kenya

    Gunmen threw grenades and opened fire at an upscale mall in Kenya's capital on Saturday, killing at least 10 people.

  • Armed police on scene.

    Armed police leave after entering the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • Mall-goers flee after attack.

    Civilians who had been hiding inside during the gun battle manage to flee from the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • An armed police officer takes cover during a bout of gunfire outside the Westgate Mall.

    The mall in Kenya's capital was hosting a children's day event at the time of the attack, a Red Cross official and witnesses said.

  • Armed police at the Westgate Mall.

    Armed police crouch down and take position during a gun battle outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • Civilians leave the mall after gun battle.

    Civilians who had been hiding during the gun battle hold their hands in the air as a precautionary measure before being searched by armed police leading them to safety, inside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • A rescue worker helps a child outside the Westgate Mall.

  • Security helps a woman outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded.

  • People flee the scene of the attack.

    Security helps people outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded.

  • A wounded man is escorted away from the mall.

    Witnesses say a half dozen grenades also went off along with volleys of gunfire in and around the mall.

  • A rescued hostage collapses on the ground after being freed by police at Westgate Mall.

    A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted.

  • Two women hug outside the mall after the attack.

    Bursts of gunfire were heard from outside the Westgate Mall Saturday, where cars were left abandoned. Witnesses say a half dozen grenades also went off along with lobbies of gunfire that started at midday.

  • Woman escapes from the Westgate Mall.

    A woman who had been hiding inside and managed to flee, sits in a state of shock, as an unidentified armed member of the security forces, above, keeps watch outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013.

  • Security officers keep a crowd under control outside the Westgate Mall

  • An injured person makes a phone call as he is helped on his arrival at the Aga Khan Hospital after the attack at the Westgate Mall.

  • An injured person arrives at the hospital after the attack on the Westgate Mall.

  • A injured child is wheeled away on a shopping trolley outside the Westgate Mall.

  • A security officer helps a wounded woman outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded. A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted. (AP Photo/Khalil Senosi)

  • An injured man arrives at the Aga Khan Hospital in Nairobi after the attack at the Westgate Mall.

  • An injured man arrives at the Aga Khan Hospital after the attack at the Westgate Mall.

    A witness to the attacks says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted. Initial police reports had described the incident as a botched robbery. Witnesses say a half dozen grenades also went off along with volleys of gunfire in and around the mall.

  • A security guard helps a child outside the Westgate Mall.

    A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted.