Kenyan troops and rescue workers are scouring the wreckage of a Nairobi shopping mall for bodies and booby-trapped explosives.

The operation comes after a four-day siege by Islamist gunmen left 67 dead and dozens more missing.

The Kenyan President announced an end to the 80-hour bloodbath late last night saying the death toll is provisional.

Three days of National mourning have been announced.

Meanwhile Somalia's Shebab insurgents claim they held 137 hostages during the siege, figures impossible to verify and higher than the number of people officially registered as missing.

The Al-Qaeda-linked fighters, in a message posted on Twitter, said "137 hostages who were being held by the mujahedeen" had died.

They also accused Kenyan troops of using "chemical agents" to end the four-day stand-off.

"In an act of sheer cowardice, beleaguered Kenyan forces deliberately fired projectiles containing chemical agents," one tweet read.

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

There was no immediate response from Kenya's government, but the Shebab have in past made repeated outlandish claims, especially on their Twitter site.

Sky's Chief Correspondent Stuart Ramsay says further blasts were heard at the Westgate mall this morning