"WHITE WIDOW?"

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

Lewthwaite is thought to have left Britain several years ago and is wanted in connection with an alleged plot to attack expensive hotels and restaurants in Kenya.

President Obama, whose father was Kenyan, said he believed the country - scene of one of al Qaeda's first big attacks, in 1998 - would continue to be a regional pillar of stability.

Somalia's prime minister appealed in Geneva on Tuesday for international support to combat al Shabaab but said a military solution to their insurgency alone was not enough.

Abdi Farah Shirdon said: "We still have a difficult journey ahead of us. A military solution alone is not enough, promotion of rule of law, greater regional cooperation and economic stability and provision of public services are all key factors."

British Defence Secretary Philip Hammond said he believed six Britons had died in the attack. Other known foreign victims are from China, Ghana, France, the Netherlands and Canada.