NAIROBI, Kenya (AP) -- Terrified shoppers huddled in back hallways and prayed they would not be found by the Islamic extremist gunmen lobbing grenades and firing assault rifles inside Nairobi's top mall Saturday. When the way appeared clear, crying mothers clutching small children and blood-splattered men sprinted out of the four-story mall.
At least 39 people were killed and more than 150 wounded in the assault, Kenya's president announced on national TV, while disclosing that his close family members were among the dead.
Foreigners were among the casualties. France's president said that two French women were killed. Two Canadians were killed, including a diplomat, said the Candadian prime minister. Four American citizens were reported injured but not killed in the attack, the State Department said Saturday.
Early Sunday morning, 12 hours after the attack began, gunmen remained holed up inside the mall with an unknown number of hostages. President Uhuru Kenyatta called the security operation under way "delicate" and said a top priority was to safeguard hostages.
As the attack began shortly after noon Saturday, the al-Qaida-linked gunmen asked the victims they had cornered if they were Muslim: Those who answered yes were free to go, several witnesses said. The non-Muslims were not.
Somalia's Islamic extremist group al-Shabab claimed responsibility and said the attack was retribution for Kenyan forces' 2011 push into Somalia. The rebels threatened more attacks.
Al-Shabab said on its Twitter feed that Kenyan security officials were trying to open negotiations. "There will be no negotiations whatsoever," al-Shabab tweeted.
As night fell in Kenya's capital, two contingents of army special forces troops moved inside the mall.
Police and military surrounded the huge shopping complex as helicopters buzzed overhead. An Associated Press reporter said he saw a wounded Kenyan soldier put into an ambulance at nightfall, an indication, perhaps, of a continuing shoot-out inside.
Witnesses said at least five gunmen -- including at least one woman -- first attacked an outdoor cafe at Nairobi's Westgate Mall, a shiny, new shopping center that includes Nike, Adidas and Bose stores. The mall's ownership is Israeli, and security experts have long said the structure made an attractive terrorist target.
The attack began shortly after noon with bursts of gunfire and grenades. Shoppers -- expatriates and affluent Kenyans -- fled in any direction that might be safe: into back corners of stores, back service hallways and bank vaults. Over the next several hours, pockets of people trickled out of the mall as undercover police moved in. Some of the wounded were trundled out in shopping carts.
"We started by hearing gunshots downstairs and outside. Later we heard them come inside. We took cover. Then we saw two gunmen wearing black turbans. I saw them shoot," said Patrick Kuria, an employee at Artcaffe, the restaurant with shady outdoor seating.
Frank Mugungu, an off-duty army sergeant major, said he saw four male attackers and one female attacker. "One was Somali," he said, adding that the others were black, suggesting that they could have been Kenyan or another nationality.
Al-Shabab, on its Twitter feed, said that it has many times warned Kenya's government that failure to remove its forces from Somalia "would have severe consequences." The group claimed that its gunmen had killed 100 people, but its assertions are often exaggerated.
"The attack at #WestgateMall is just a very tiny fraction of what Muslims in Somalia experience at the hands of Kenyan invaders," al-Shabab said. Another tweet said: "For long we have waged war against the Kenyans in our land, now it's time to shift the battleground and take the war to their land #Westgate."
Al-Shabab's Twitter account was suspended shortly after its claim of responsibility and threats against Kenya. Twitter's terms of service forbids making threats.
Al-Shabab threatened in late 2011 to unleash a large-scale attack in Nairobi. Kenya has seen a regular spate of grenade attacks since then but never such a large terrorist assault.
Nairobi's mortuary superintendent, Sammy Nyongesa Jacob, said Africans, Asians and Caucasians were among the bodies brought to the mortuary.
The U.S. State Department condemned "this senseless act of violence that has resulted in death and injury for many innocent men, women, and children."
In a separate statement, a White House spokeswoman said some staff at the U.S. Embassy in Kenya have been "tragically affected" by the attack. No other information was provided.
"The perpetrators of this heinous act must be brought to justice, and we have offered our full support to the Kenyan Government to do so," Caitlin Hayden, a spokeswoman for the White House National Security Council, said in the statement.