The US has admitted it has lost track of Osama Bin Laden, a month after believing he was trapped in caves.
Officials say Washington is becoming increasingly frustrated over the lack of information on where he is.
The most recent sign of him was in early December, when agents believe they overheard him directing troops by radio in Tora Bora, Afghanistan.
Defence Secretary Mr Donald Rumsfeld has accused Iran of allowing other al-Qaeda fighters to escape to the west, but the White House believes bin Laden is alive and hiding in either southeastern Afghanistan or in Pakistan.
US security officials say if the terrorist leader had died, the remnants of the al-Qaeda network would be overheard discussing his death in telephone or radio transmissions.
Another reason he is believed to be alive, officials said, is that there has been no convincing evidence that he is dead, despite a £17.5 million sterling reward for such information.
With bin Laden remaining elusive, President Bush has recast his war aims. "Osama bin Laden is not my focus," he said. "My focus is terror at large". In his State of the Union speech, Mr Bush did not even mention bin Laden by name, simply delivering a general warning to terrorists.
"I think everyone knew from the beginning how hard it was going to be to get one person, and we knew we shouldn't put so much emphasis on Osama bin Laden," said one American official. "But it is too late for that now".