Pakistan has captured most of bin Laden's lieutenants, including 9/11 attacks coordinator Khalid Sheikh Mohammed, and claims to have reduced the remaining al-Qaida command to mere figureheads. Pakistan has lost 350 troops fighting al-Qaida and Taliban-linked militants.

Yet Afghan officials allege that Pakistan is sanctuary for Taliban rebel leaders and lets them recruit from radical Islamic schools. They even suggest that Pakistan is hiding bin Laden, perhaps to ensure Pakistan remains of strategic importance to Washington.

"We believe he is being kept as a prize, as an ultimate bargaining chip," said a senior Afghan government official, who declined to be identified due to the sensitivity of his comments.

Latfullah Mashal, a former Afghan Interior Ministry spokesman, goes so far as to pinpoint bin Laden's hideout in a remote valley in Pakistan's North Waziristan region. He says there's a mountain fortress with a network of tunnels, guarded by African militants who never venture outside.

Pakistan, which formally ended its support for the Taliban after the Sept. 11 attacks, rejects both allegations. It has about 80,000 troops in its wild tribal regions along the Afghan frontier, including a U.S.-trained and equipped quick-reaction force.

"I don't think any other country has played a bigger role than Pakistan," said Interior Minister Aftab Khan Sherpao.

Retired Lt. Gen. Ali Mohammed Jan Aurakzai, who led the Pakistani army into the region after the Sept. 11 attacks, said sealing the border between Afghanistan and Pakistan would require between 150,000 and 200,000 troops "and still there's no 100 percent guarantee that infiltration would not take place."

Strained by the demands of Iraq, the U.S. has only about 20,000 troops in Afghanistan. The roughly 10,000 in the border area must cover about 30,000 square miles of some of the most forbidding territory on Earth: jagged mountains, both arid and forested, that become impassable in winter. There are steep valleys and rushing rivers spanned by rickety rope bridges; dark caves that could be booby trapped. Deeply religious and xenophobic villagers also obstruct efforts to run down al-Qaida remnants.

"Bin Laden has a network of contacts and places to go to if he needs to that's pretty close to 20 years old. He's a veteran of that region, so it's very hard to find him," said Michael Scheuer, former chief of the CIA's now-disbanded unit dedicated to hunting the al-Qaida leader. "Bin Laden's status as a hero in the Islamic world is also a telling factor in why he's not been caught."