Sources: Pakistan Allows U.S. 'Hot Pursuit'

Dec. 19 -- The United States has struck a secret agreement with Pakistan to allow "hot pursuit" of al Qaeda fighters fleeing across the border from Afghanistan, sources told ABCNEWS.

The deal will allow U.S. troops to hunt the fighters on the ground and fire on them from the air, but sources said it will also be on a case-by-case basis, with the United States required to ask permission each time.

Hundreds of al Qaeda fighters are believed to be trying to escape into Pakistan after the fall of their Tora Bora mountaintop complex earlier this week, and there are suspicions that Osama bin Laden may be among them.

"He's either dead in some tunnel or he's alive. ... And it does not matter. We'll find him one day and we'll know what's happened," U.S. Defense Secretary Donald Rumsfeld told a Pentagon briefing today.

In the last two days, U.S. and Pakistani sources say nearly 400 suspected al Qaeda members have been picked up by Pakistani patrols.

Meanwhile, U.S. forces continued to comb through the caves and tunnels that comprise Tora Bora, looking for al Qaeada fighters still in hiding and other clues to the whereabouts of bin Laden, the prime suspect for the Sept. 11 attacks.

In an effort to step up the search, hundreds of U.S. Marines will be sent to the area in the next few days, sources told ABCNEWS.

"There is a lot of information that is being collected as U.S. and opposition forces move through various towns and … caves," National Security Council spokesman Sean McCormack said. "They're looking at the information to see what can be used to further our military objectives."

U.S. warplanes flew some 20 sorties today but for the second straight day dropped no bombs, instead conducting surveillance over the densely wooded mountains near Afghanistan's eastern border with Pakistan.

Captive Intelligence

According to Eastern Alliance commander Afta Gul, some captives "are telling us stories about Osama giving a speech 14 days ago and then leaving, but these men are not very credible. I have heard that Osama has shaved his beard and gone to Pakistan, but no one can say for sure."

Intelligence sources told ABCNEWS they believe they have some of bin Laden's most senior people in custody.

Although officials, lacking photographs and fingerprints, had some problems identifying these individuals among the bedraggled masses, sources said other prisoners are starting to finger their former leaders and provide information as to where bin Laden might be.