Westgate Nairobi
Kenya Defence Forces soldiers comb the Westgate shopping mall in Nairobi (Reuters)

The Islamist terrorist group that took over Nairobi's most prestigious shopping mall for four days has claimed that Kenyan troops used nerve gas to retake the building and killed more than 100 hostages in the process.

Somalia-based al-Shabaab said that the Kenyan government was responsible for the deaths of 137 shoppers, sales staff and tourists. The corpses had been deliberately buried under the rubble after parts of the Westgate shopping centre collapsed in an explosion, said the militants.

The official death toll stood at 72 but not all victims' bodies have been recovered yet.

The government denied al-Shabaab's claims which were made in a series of tweets from an account believed to be genuine.

"Having failed to defeat the mujahideen inside the mall, the Kenyan govt disseminated chemical gases to end the siege at #Westgate Mall," the account @HSM_PR tweeted.

"To cover their crime, the Kenyan govt carried out a demolition to the building, burying evidence and all hostages under the rubble," it added.

@HSM_PR was used to tweet the first picture of Islamist gunmen inside the mall and had been created after other domains believed to be run by the terrorist cell were suspended for breaching Twitter regulations.

Kenyan government spokesman Manoah Esipisu denied that any chemical agent, including teargas, had been used to retake control of the mall.

Esipisu said that the top floors collapsed because of by a fire set by the terrorists.

"Al-Shabaab is known for wild allegations and there is absolutely no truth to what they're saying," he said.

Kenyan security officials had earlier said they had blown up part of the roof to get inside the besieged shopping centre.

President Uhuru Kenyatta confirmed that three floors of the four-storey building had collapsed during the rescue operation and that a number of bodies were still trapped under the rubble.

Seventy-two people - 61 civilians, six security officials and five terrorists - have been confirmed as dead but officials said the number was likely to rise, as clear-up operations continued. More than 170 people were injured.

Authorities were investigation whether foreign and/or Western nationals were among the attackers. Kenyatta said he could not confirm intelligence reports that three Americans and one Briton had taken part in the terrorist operation.

Experts from the US, UK, Germany, Canada and Interpol have joined the investigation, Kenya's interior minister Joseph Lenku said.

Foreign minister Amina Mohamed said that a Briton, widely believed to be Samantha Lewthwaite, 29, the so-called White Widow, was involved.

Al-Shabaab dismissed that claim and said all the attackers were male.

"Kenyan govt is capitalising on story of a woman allegedly involved in #Westgate so as to curry favour with the British govt," @HSM_PR tweeted.

Eleven suspects, including at least seven at Nairobi's airport, have been arrested.

Among them was a British citizen, the British Foreign Office has confirmed. The UK ambassador to Kenya said that the man was "not of significant interest" to the investigation into the attack on the mall.


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