Nairobi, Kenya (CNN) -- Three floors of the Westgate Mall in Nairobi collapsed during efforts to clear terrorists who had laid siege to the building for four days, trapping bodies inside, President Uhuru Kenyatta said in a televised address Tuesday.
Five of the gunmen were killed in the fighting, Kenyatta said. Eleven other people had been arrested over possible connections to the attack, which left 61 civilians and six security officers dead, 62 people in the hospital and Kenya's reputation as a bulwark of African stability in tatters.
"We have ashamed and defeated our attackers," he said in the address, which capped a four-day ordeal in which Kenyan forces battled Al-Shabaab terrorists for control of the upscale mall.
Earlier in the day, sporadic gunfire could be heard coming from the mall as authorities made their final sweeps through the building.
Some 175 people had been injured, the Kenya Red Cross said.
The fate of civilians who may have still been hiding inside the mall or held hostage by terrorists remained unclear. Earlier, Kenyan authorities had said they believed all hostages had been freed, but the Red Cross said 65 people remained unaccounted for.
The harrowing episode began midday Saturday in Nairobi when some 10 to 15 gunmen stormed the mall, shooting indiscriminately, according to witness accounts.
Witnesses said the gunmen went from store to store, shooting people, and then took hostages.
Mwagi Dorcas told CNN's "New Day" on Tuesday that she hid behind luggage in the mall's ground-floor grocery store, memorizing a Muslim prayer sent to her by family in a desperate bid to save her life should attackers find her. Al-Shabaab and some witnesses have said the attackers quizzed shoppers about their faith before deciding whether to kill them, releasing Muslims and targeting many others.
"I was praying the whole time," she said. "I believed that, you know, if I got out, I would be rescued."
Some were spared despite not being Muslim. In one remarkable case reported by The Sun newspaper in Britain, terrorists spared a 4-year-old boy who confronted them, saying, "You're a very bad man."
Al-Shabaab claimed the attack was in retribution for Kenya's involvement in an African Union military expedition that has bruised the terror group in its Somali homeland.
"We have an idea who these people are, and they are clearly a multinational collection from all over the world," Gen. Julius Karangi, chief of Kenya Defense Forces, told reporters Monday in Nairobi. "This is not clearly a local event. We are fighting global terrorism here."
Law enforcement sources said Monday they were scouring intelligence reports for evidence of a U.S. connection to the attack, but a senior U.S. official said Monday the claim was looking less solid as they continued to investigate.
Most of the 62 known dead civilians are Kenyans, authorities said. Six British citizens, two French nationals, two Indians and two Canadians, including a diplomat, also died, their governments said.
Those killed include:
• Dutch national Elif Yavuz, a senior vaccines researcher for the Clinton Health Access Initiative based in Tanzania. Yavuz was pregnant and expecting her first child in October, said Julio Frenk, dean of faculty at the Harvard School of Public Health. "Elif was brilliant, dedicated, and deeply admired by her colleagues, who will miss her terribly," the Clinton family said in a statement.
• Yavuz's husband, Australian-British architect Ross Langdon, who moved to Nairobi to build sustainable architecture for Africa, volunteering to build hospitals and clinics free of charge.
• Kofi Awoonor, a renowned African poet, author and Ghanian statesman. Awoonor earned his doctorate from New York's Stony Brook University and was a professor of literature there in the 1970s.
• A nephew of Kenya's president along with the nephew's fiancee.
• A Peruvian doctor, Juan Jesus Ortiz, who had previously worked for the U.N. Children's Fund and lived in Kenya doing consulting work.
• Sridhar Natarajan, an Indian national and employee of a local pharmaceutical firm, and 8-year-old Paramshu Jain, the son of a bank branch manager, CNN sister network CNN-IBN reported, citing officials in India.
Al Qaeda connection?
The mall siege is the deadliest terror attack in Kenya since al Qaeda blew up the U.S. Embassy there in 1998, killing 213 people.
On Monday, Kenya's foreign minister told CNN it's clear that Al-Shabaab was not acting alone.
"This bears the hallmarks of al Qaeda," Foreign Minister Amina Mohamed said. "This is not just Al-Shabaab. In fact, the leaders are not Somali, as you may have heard. This was al Qaeda. It was a very well-coordinated effort."
CNN's Michael Pearson reported and wrote from Atlanta. Zain Verjee and Arwa Damon reported from Nairobi. CNN's Nima Elbagir, Victoria Eastwood, Atika Shubert, Becky Anderson, Lillian Leposo, Brian Walker and Holly Yan also contributed to this report.