Foreign fighters

Kenyatta said he could not confirm intelligence reports of British and American militants, adding that forensic tests were being carried out to establish their nationalities. The government denied speculation that women were among the guerrillas, but said some had been dressed as women. That may have been a ploy to smuggle more weapons past mall guards.

It is unusual, if not unknown, for Islamist militants to use female fighters: "We have an adequate number of young men who are fully committed and we do not employ our sisters in such military operations #Westgate," al Shabaab said on Twitter.

It also dismissed comments by a Kenyan minister that two or three of the militants were young Somali or Arab Americans.

A British security source said it was possible that Samantha Lewthwaite, widow of Germaine Lindsay one of the London suicide bombers of July 7 2005, was involved in the Nairobi siege in some way. "It is a possibility. But nothing definitive or conclusive yet," the source said.

Lewthwaite is wanted in connection with an alleged plot to attack expensive hotels and restaurants in Kenya.

Making no mention of gunmen still in the mall, al Shabaab also drew a link to the most recent Islamist attack in London, when a soldier was stabbed to death on a busy street in May in the suburb of Woolwich. Michael Adebolajo and a fellow British Muslim convert of Nigerian descent face trial for murder.

"It's an eye for an eye and a tooth for a tooth...' Remember Mujahid Adebolajo? This is what he meant. His was #Woolwich, #Westgate ours!" read another al Shabaab Twitter post.

"These cowards will meet justice as will their accomplices and patrons, wherever they are," said Kenyatta.