Kenyan security forces and foreign forensic teams are examining the scene of an attack by Somali militants on a Nairobi shopping mall that killed at least 72 people, authorities have said.
Joseph Ole Lenku, Kenya's interior minister, said on Wednesday several bodies of al-Shabab fighters might be under the rubble in Nairobi's Westgate shopping mall and that the government now believed that at least 10 of the attackers had been killed.
Lenku's remarks came as forensic teams continued to go from room to room in an attempt to secure the complex, a day after the 40-hour siege by the armed Somali group that killed dozens ended.
"It is an elaborate process," he said.
"Among the things that are going on now are fingerprinting, DNA identification [and] ballistic examinations."
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Lenku said the evidence collection would take at least a week.
Forensic experts and investigators from Britain, the US, Israel, Germany, Canada and Interpol have joined the probe, he said.
The siege began midday on Saturday, when al-Shabab fighters marched into the building, firing from automatic weapons and throwing grenades.
Although the situation inside the mall on Wednesday was not considered secure, a city morgue official said his workers were preparing to go into the building soon.
Officials said the death count would probably rise. Estimates varied between only a few bodies to dozens of bodies possibly still inside the mall.
Al Jazeera's Andrew Simmons, reporting from Nairobi, said: "Some are predicting it could go well beyond the hundred mark, possibly even double the death toll."
Against this grim backdrop, Kenya began three days of national mourning for the victims of the attack on Wednesday.
President Uhuru Kenyatta told the nation the night before that the attackers had been defeated.
Fears persist, however, that some of the attackers could still be alive and loose inside the rubble of the mall, a vast complex that had shops for international retailers, as well as banks, restaurants and a casino.
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For its part, al-Shabab has accused the Kenyan government forces of using chemical weapons in their assault on the building, then carrying out "a demolition'' that buried 137 hostages.
In a series of Twitter posts from an account believed to be genuine, al-Shabab said that "having failed to defeat the mujahideen inside the mall, the Kenyan government disseminated chemical gases to end the siege".
They said "to cover their crime, the Kenyan government carried out a demolition to the building, burying evidence and all hostages under the rubble".
Manoah Esipisu, a government spokesperson, dismissed the accusation, telling the AP news agency that no chemical weapons were used and that the official civilian death toll was still 61.
He said several floors of the mall collapsed after a fire started by al-Shabab fighters caused structural weakness in a third floor parking lot, which then came down onto the second floor and brought it down onto the first or ground floor.
"Al-Shabab is known for wild allegations and there is absolutely no truth to what they're saying," he said.