"Where he is, is a question mark. The trail has gone cold as to whether he's still in the caves of Tora Bora or, in fact, has slipped into Pakistan" across the rugged 1,500-mile border, Graham said, declining to discuss details of the intelligence.

The Tora Bora mountain complex, 30 miles south of Jalalabad, was captured by U.S.-backed forces opposing Afghanistan's Taliban militia on Dec. 6 after some of the heaviest bombing of the campaign, which began on Oct. 7.

On Friday, President Bush said he had no idea where bin Laden was -- or whether he had survived "in a cave with the door shut or a cave with the door open."

Appearing tired, gaunt and gesturing with his right hand only, though reportedly left-handed, bin Laden was last heard from publicly in a videotape that surfaced on Wednesday and was apparently taped earlier this month.

SOLDIERS RELIEVE MARINES

The Pentagon said on Sunday that the U.S. Marine vanguard force in southern Afghanistan was being relieved by an Army air assault unit to free the Marines for unspecified new missions.

Elements of the Army's 101st Airborne Division, headquartered at Fort Campbell in Kentucky, have been ordered to deploy to Afghanistan as part of the campaign to crush surviving al Qaeda guerrillas and their Taliban allies, the Pentagon said.

"These forces will relieve the Marine Corps forces in the Kandahar area to allow the Marines the opportunity to prepare for future missions," said Marine Lt. Col. Michael Humm, a Pentagon spokesman.

The Pentagon did not say when the changeover would be completed. More than 1,000 Marines -- drawn from the 15th and 26th Marine Expeditionary Units -- have been deployed in southern Afghanistan since their advance elements set up a bridgehead called Camp Rhino within striking distance of Kandahar airport on Nov. 25.

The Marines rolled into Kandahar, the former Taliban stronghold, on Dec. 13, securing the airport and establishing a makeshift prison where 139 battlefield "detainees" were being held as of Sunday.

Graham said he had received no intelligence on the physical condition of bin Laden, the Saudi-born militant accused of masterminding the Sept. 11 attacks that killed more than 3,000 people in the United States.

A spokesman for the CIA, Fred Leeder, declined to comment on any intelligence suggesting bin Laden was still alive.

COMPLEX NEAR GARDEZ BOMBED

The Pentagon said U.S. bombers had hit a suspected Taliban leadership complex outside the eastern Afghan city of Gardez.

Two Air Force B1-B bombers fired precision-guided missiles on Friday night at the compound, located 10 miles from Gardez in Paktia Province, in the latest reported airstrike, military officers said.

"Indications are that we did hit what we were aiming at," said Marine Lt. Col. Dave Lepan, a Pentagon spokesman, without identifying those targeted.

In Kabul, Defense Minister Mohammad Fahim said on Friday that bin Laden probably had escaped to Pakistan with virtually all surviving al Qaeda fighters, making more airstrikes pointless, in his view.

The number of suspected Taliban and al Qaeda fighters being held by the U.S. military has risen to 150, the U.S. Central Command, which is running the campaign, said on Sunday.

Of the total, 139 were being detained at a makeshift jail built by Marines at Kandahar airport, including 14 brought on Saturday from Shiburghan, west of Mazar-i-Sharif, said Air Force Lt. Col. Martin Compton, a Central Command spokesman.

Two others were being held at Bagram air base, north of Kabul, and one in Mazar-i-Sharif, the command said. Eight more, including American John Walker Lindh, were being held on the amphibious assault ship USS Peleliu in the Arabian Sea.

The United States has begun preparations to bring an undetermined number of al Qaeda and Taliban prisoners to the U.S. Naval Station at Guantanamo Bay on Cuba's southeast tip for further interrogation. Some may be candidates for planned U.S. military tribunals that might try them on terrorism-related charges.

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