NAIROBI, Kenya -- Terrorists who carried out the attack on the Westgate shopping mall here claimed Wednesday that 137 hostages were buried in the rubble of collapsed sections of the building.
Shabab also claimed via a Twitter account that Kenyan authorities had lobbed "chemical agents" into the mall, killing dozens of hostages, as the effort to retake the shopping center reached its climax.
Government spokesman Manoah Esipisu rejected the claims.
"Al Shabab is known for wild allegations, and there is absolutely no truth to what they're saying," he told the Associated Press.
Seeking to take advantage of the vacuum of information about the fate of hostages and other key questions, Shabab also posted a series of tweets Wednesday that accused Kenyan forces of toppling the building.
The government of President Uhuru Kenyatta blames the collapse of three floors on a fire it says was started by the terrorists.
"Kenyatta and his govt are to be held culpable for Westgate and for the lives of the 137 hostages who were being held by the Mujahideen," Shahab tweeted Wednesday.
"In an act of sheer cowardice, beleaguered Kenyan forces deliberately fired projectiles containing chemical agents into building," the group said.
"To cover their crime, the Kenyan govt carried out a demolition to the building, burying evidence and all hostages under the rubble."
The government has said just a few civilians remained in the building when it collapsed. It has confirmed that 61 civilians, six soldiers and five gunmen died in the assault.
Kenyan authorities have arrested 11 suspects, including one British man who was arrested at the airport on his way out of Kenya, according to local media.
Flags were at half-mast Wednesday as the nation began three days of mourning. Meanwhile, Kenyans began to question the contradictions and paucity of information from government officials on what happened in the incident, as well as the intelligence and security failures that led to the siege.
Many questioned how a group of about 15 terrorists managed to seize the mall and hold off security forces for four days.
During the siege, an information war raged, with Kenyan authorities tweeting about the event and issuing what turned out to be premature claims of victory, as gunfights continued in the mall.
A Kenyan police constable was charged Wednesday with the theft of a blood-stained wallet containing credit cards and photographs of one of the victims, a Kenyan newspaper, the Daily Nation, reported.
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Special correspondent Soi reported from Nairobi and Times staff writer Dixon from Johannesburg, South Africa.