The militant group that attacked a Nairobi mall and killed at least 60 people says it is still holding hostages alive inside and that its fighters are "still holding their ground." 

The Twitter messages posted Tuesday by the al-Qaeda-linked rebel group al-Shabaab came after Kenyan government assurances of success in the fourth-day of the standoff.

Al-Shabaab says the hostages "are still alive, looking quite disconcerted but, nevertheless, alive."

A security expert with contacts inside said Monday night there were at least 30 hostages when the assault began Saturday and at least 10 were believed to be still inside the upscale mall. Officials did not give a figure, saying only that "most" hostages had been released.

Sporadic gunfire could be heard from the building Tuesday as government forces pressed on inside.

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.

Americans, Briton involved, says official

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.

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.

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Annemarie Desloges, left, was killed when Somali militants attacked an upscale mall in Nairobi, Kenya on Saturday. Her husband Robert Munk, right, was also injured. (Facebook)

However, there were at least 30 hostages when the assault by al-Shabaab 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.

Flames and dark plumes of smoke rose Monday above the Westgate shopping complex for more than an hour after four large explosions rocked the surrounding neighbourhood. The smoke was pouring through a large skylight inside the mall's main department and grocery store, where mattresses and other flammable goods appeared to have been set on fire, a person with knowledge of the rescue operation told The Associated Press.

The explosions were followed by volleys of gunfire as police helicopters and a military jet circled overhead, giving the neighbourhood the feel of a war zone.

Fate of hostages unclear

By Monday evening, Kenyan security officials claimed the upper hand.

"Taken control of all the floors. We're not here to feed the attackers with pastries but to finish and punish them," Police Inspector General David Kimaiyo said on Twitter.

Naguib Damji

Vancouver-area businessman Naguib Damji has been identified by family members as one of the Canadians killed in the mall attack in Kenya. (Courtesy Karima Damji/Facebook)

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.

An al-Shabaab spokesman, Sheik Ali Mohamud Rage, said in an audio file 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.

The attackers have lots of ammunition, the militant group said in a Twitter feed, adding that Kenya's government would be responsible for any loss of hostages' lives.

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."

2 Canadians killed

At least 62 people were killed in the assault Saturday by some 12 to 15 al-Shabaab militants 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.

Westgate mall layout, Nairobi, Kenya

The Westgate mall attack in Nairobi, Kenya explained in five steps. Kenya's national police service said on Monday, Sept. 23 that officers had regained control of the mall where al-Qaeda-linked militants launched a savage attack Saturday, killing a reported 62 people, including two Canadians.

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.

Canadian officials have also confirmed that at least two Canadian citizens were among the 175 injured in the attack at the upscale shopping mall. A spokesperson for Foreign Affairs confirmed that two Canadians were killed and two were injured and remain in hospital following the attack.

John Babcock said Monday that consular officials had been in contact with the families and continue to provide assistance as required.

"For privacy reasons, we are not able to release any further details," Babcock said in an email.

A Minnesota woman identified the injured Canadians as her nieces Fardosa Abdi, 17, and Dheman Abdi, 16. She told The Associated Press that the girls were shopping when the siege started. 

She said Fardosa is in critical condition after undergoing two surgeries for severe leg injuries, while Dheman had a bullet break her leg and an explosion injure her arm. Hassan said the teens are Canadian citizens who moved three years ago to Nairobi, where their father has a real estate business.

Several federal departments confirmed that one of the dead Canadians was Annemarie Desloges, 29, a diplomat who worked at the Canadian Embassy. Desloges was previously posted in Delhi and was off-duty, shopping at the mall Saturday when the militants attacked.

Desloges has worked for both Citizenship and Immigration Canada (CIC) as well as the Canada Border Services Agency in Kenya, the offices confirmed in a joint statement Saturday night. She joined the CIC in 2006, then the foreign service in 2008.

Another Canadian who died in the attack at the upmarket shopping centre has been identified by Vancouver-area family members as Naguib Damji.

Al-Shabaab draws recruits from abroad

Fighters from an array of nations participated in the assault, according to Kenya's Chief of Defence 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.

Al-Shabaab, whose name means "The Youth" in Arabic, said the mall attack was in retribution for Kenyan forces' 2011 push into neighbouring Somalia. It was the deadliest terrorist attack in Kenya since the 1998 al-Qaeda truck bombing of the U.S. Embassy in Nairobi, which killed more than 200 people.

An extremist Islamic force that grew out of the anarchy that crippled Somalia after warlords ousted a longtime dictator in 1991, al-Shabaab is estimated to have several thousand fighters, including a few hundred foreigners, among them militants from the Middle East with experience in the Iraq and Afghanistan conflicts. Others are young, raw recruits from Somali communities in the United States and Europe.

For years Minnesota has been the centre of a federal investigation into the recruiting of fighters for al-Shabaab. Authorities say about two dozen young men have left Minnesota since 2007 to join the group. Minnesota's Somali community is the largest in the U.S.

Somali President Hassan Sheikh Mohamud said the attack showed that al-Shabaab was a threat not just to Somalia but to the international community.

Mohamed, the Kenyan foreign minister, said her country needs to work with other governments to fight the increasing terrorist threat and "much more with the U.S and the U.K., because both the victims and the perpetrators came from Kenya, the United Kingdom and the United States.

"That just goes to underline the global nature of this war that we are fighting," she said.

Reports that some of the attackers may have been Somalis who lived in the United States illustrate the global nature of the militant group, the Somali leader said in a speech at Ohio State University. "Today, there are clear evidences that Shabaab is not a threat to Somalia and Somali people only," he said. "They are a threat to the continent of Africa, and the world at large."

As the crisis passed the 48-hour mark, a video emerged that was taken by someone inside the mall's main department store when the assault began. It showed frightened and unsure shoppers crouching as long, loud volleys of gunfire could be heard.

Kenyans in many parts of the country stood in long lines Monday to donate blood to aid the nearly 200 people injured in the attack. Fundraisers raised hundreds of thousands of dollars, though government officials warned of scam artists taking advantage of the tragedy.

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An aerial view and map of the Westgate shopping centre in Nairobi, where an attack killed at least 59 people on Saturday. (Google/CBC News)