An image grab taken from AFP TV shows Kenyan troops taking position on September 21, 2013 inside the Westgate mall in Nairobi. (Nichole Sobecki/AFP/Getty Images)
NAIROBI, Kenya (NBC) -- Kenya's president Tuesday said security forces have killed five terrorists and arrested 11 suspects in connection with the horrific siege on a Nairobi shopping mall, bringing to a close four days of chaos and carnage.
The al Qaeda-linked attackers - believed by Kenyan officials to include "two of three Americans" and a British woman - staged a shooting massacre that killed some 61 civilians and 6 security officers and shattered countless lives. However, President Uhuru Kenyatta said he could not confirm reports of American or British involvement in the attack.
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Kenyatta said that Wednesday will mark the beginning of three days of national mourning. Some 62 people have been operated on in the wake of the siege and remain in the hospital, he said.
His announcement Tuesday capped off hours of uncertainty, as security officials said that they had gained ground on the heavily-armed militants from the Somalia-based al-Shabaab while the al Qaeda-affiliated group claimed in an unverified Twitter post that they were "still holding their ground" inside the luxury Westgate complex.
It also posted a security video image that it said showed its members "strolling around the mall."
Al Shabaab regularly changes its Twitter handle as its accounts are frequently suspended. Earlier, Kenya's Interior Ministry had tweeted that security forces were "in control of Westgate."
Amina Mohamed, Kenya's foreign minister, told PBS Newshour late Monday that American and British citizens of Somali or Arab origin were believed to be among the perpetrators "from the information that we have."
She said the Americans were "young men, about between maybe 18 and 19" years old and lived in "in Minnesota and one other place."
However, a senior U.S. law enforcement official told NBC News that authorities had been unable to verify that Americans were involved, despite aggressive checks of travel records.
"That doesn't mean it's not true. We just have no information to go on," the official said.
A British woman was also involved, Mohamed said - fueling speculation that Samantha Lewthwaite, the widow of a suicide bomber who attacked London's transit system in 2005, was linked to the Kenya siege.
According to Reuters, al Shabaab denied that Westerners were involved in the attack.
"Those who describe the attackers as Americans and British are people who do not know what is going on in Westgate building," Reuters quoted the group's media office as saying.
As the standoff wore on, the survivors' stories emerged.
Some of them took to Twitter: Kamal Kaur, a journalist for Radio Africa, chronicled the ordeal in a heartbreaking series of posts and said she could not stop thinking about a little boy who was shot instead of her own son.
The bullet missed her son by an inch, she wrote - "almost had his head blown off" - then bounced off a wall and struck and killed the other boy.
"Image of the boy I was trying to save but got shot instead of my son keeps swimming in front of my eyes," Kaur wrote, in posts collected by The Independent, a British newspaper. "How do I sleep after seeing that?"
The journalist spoke of dried blood in her hair, dead bodies and wailing victims.
"Bodies of children were everywhere," she wrote. "Children. Innocent little children. Holding on to me asking where their mummies were."
Kaur's colleague and friend Ruhlia Adatia, six months pregnant, was killed in the siege. Kaur wrote on Twitter about breaking the news to her own children about Adatia, known to them as Ruhlia Auntie.
"I still haven't told my children that their Ruhila Auntie is no more. I don't know how to. I can't. They're still in shock & wounded."
Five Americans were reported injured in the mall attack, including a San Diego woman. Among the dead were four Britons and a Canadian diplomat, and British Prime Minister David Cameron said: "We should prepare ourselves for further bad news."
Al Shabaab is an Islamist terrorist force that grew out of the anarchy that crippled Somalia after warlords ousted a longtime dictator in 1991. Its supporters include many Somalis living in other countries including the U.S. and Britain.
Kenya has sent troops to Somalia as part of an African Union force trying to stabilize the country, which was long without a functioning government, and push back al Shabaab.
The United Nations envoy for Somalia called on Tuesday for additional African troops to counter al Shabaab, which he said numbered some 5,000 people and posed an international threat.
"Security remains the number one challenge, the control and defeating of al Shabaab is key to this," Nicholas Kay, U.N. special representative for Somalia, told reporters in Geneva, Reuters reported.
President Obama told the United Nations General Assembly on Tuesday morning that the attack "indicates the dangers that remain" in the global fight against terrorism.
Obama told dignitaries and envoys from some 200 member states that al Qaeda has broken into regional networks and militias, which presents "serious threats to governments, diplomats, businesses and civilians across the globe."