NAIROBI, Kenya -- Kenya's military said late Sunday it had rescued "most" of the remaining hostages held by al-Qaida-linked terrorists in an upscale Nairobi mall after launching a major operation to end a two-day standoff that already had killed 68 people.
The military assault, which began shortly before sundown, came as two helicopters circled the mall, with one skimming very close to the roof. A loud explosion rang out, far larger than any previous grenade blast or gunfire volley.
Kenyan police said on Twitter that a "MAJOR" assault had started to end the bloody siege.
"This will end tonight. Our forces will prevail. Kenyans are standing firm against aggression, and we will win," Kenya's National Disaster Operation Centre said on Twitter.
Kenya Defense Forces later said it had rescued most hostages and had taken control of most of the mall.
Many of the rescued hostages -- mostly adults -- were suffering from dehydration, Col. Cyrus Oguna, a military spokesman, told The Associated Press. Oguna refused to make public the number of hostages rescued or of those still being held. He said some of the attackers had, "most probably," been killed in the operation, which began in the morning and culminated in the evening.
The assault came about 30 hours after 10 to 15 al-Shabab extremists stormed the mall Saturday from two sides, throwing grenades and firing on civilians.
Loud exchanges of gunfire emanated from inside the four-story upscale mall throughout Sunday. Kenyan troops were seen carrying in at least two rocket-propelled grenade launchers. The al-Shabab terrorists reacted angrily to the helicopters on Twitter and warned that the Kenyan military action was endangering hostages.
Kenyan officials said they would do their utmost to save hostages' lives but no officials could say precisely how many hostages were inside. Kenya's Red Cross said in a statement citing police that 49 people had been reported missing. Officials did not make an explicit link but that number could give an indication of the number of people held captive.
The Red Cross said the death toll on Sunday rose to 68 after nine bodies were recovered in a joint rescue mission.
A U.S. State Department spokeswoman condemned the "despicable massacre of innocent men, women and children." U.S. law enforcement, military and civilian personnel in Nairobi were providing advice and assistance, as requested by Kenya, spokeswoman Marie Harf said.
Al-Shabab claimed responsibility for the attack that specifically targeted non-Muslims. The attackers apparently included some women. The Islamic extremists said the attack was retribution for Kenyan forces' 2011 push into neighboring Somalia, al-Shabab's home country.
Al-Shabab said on its new Twitter feed -- after its previous one was shut down Saturday -- that Kenyan officials were asking the hostage-takers to negotiate and offering incentives.
"We'll not negotiate with the Kenyan govt as long as its forces are invading our country, so reap the bitter fruits of your harvest," al-Shabab said in a tweet.
Kenyan President Uhuru Kenyatta reiterated his government's determination to continue fighting al-Shabab.
"We went as a nation into Somalia to help stabilize the country and, most importantly, to fight terror that had been unleashed on Kenya and the world," said Kenyatta. "We shall not relent on the war on terror."
He said that although this violent attack had succeeded, the Kenyan security forces had "neutralized" many others. Earlier in the day, Kenyatta said his nephew and his nephew's fiance were killed in the attack.