Britain still expects to find Osama bin Laden in Afghanistan, Downing Street said on Monday.

Speaking after the US was forced to admit that it did not know where the al Qaeda leader was, Number 10 said it had no evidence to suggest he had fled Afghanistan.

"It is self evident that we haven't got him yet, the hunt goes on and we will keep on," said a spokesman. "Our assumption is that he remains in Afghanistan."

The comments followed suggestions that the Saudi-born dissident had fled the Tora Bora camp before the US onslaught late last week.

Some reports now suggest that bin Laden has fled Afghanistan and has made his way over the border into Pakistan.

The US, which had previously declared that it was hot on the heels of bin Laden, has now admitted that the trail has gone cold.