Troops set up efforts to track down bin Laden

United States troops are stepping up their efforts to establish the fate of Osama bin Laden.

After a brief rest over Christmas, US forces are going back into the caves of the Tora Bora area of eastern Afghanistan to search for clues as to bin Laden's whereabouts.

Up to 500 Marines may be drafted in to scour the caves, which were al-Qaida's last major stronghold until recent attacks.

Since then nothing has been heard of the Saudi-born militant, the prime suspect in the September 11 attacks on the United States.

Coalition sources have said it is "quite possible" that bin Laden was killed in the onslaught on Tora Bora.

But they acknowledge that they are not sure about his fate, and there are suspicions that he may have fled Afghanistan, possibly into neighbouring Pakistan.