AFGHANISTAN-PAKISTAN BORDER — The al-Qaida terror camps are gone from Afghanistan, but the enigma of Osama bin Laden still hangs over these lawless borderlands where tens of thousands of U.S. and Pakistani troops have spent nearly five years searching for him.

Villagers say the CIA missed by only a few miles when it targeted bin Laden’s top deputy, Ayman al-Zawahri, with a missile strike in January. Then in May, U.S. Special Forces arrested one of al-Zawahri’s closest aides, suggesting the trail has not gone entirely cold.

As for bin Laden himself He may be nearby. Yet hopes of cornering the Saudi-born al-Qaida leader seem distant as ever. The last time authorities said they were close to getting him was in 2004, and in hindsight those statements seem more hope than fact.

Five years after the Sept. 11 attacks, the most publicized manhunt in history has drawn a blank. The CIA has dismantled its unit dedicated to finding the al-Qaida chiefs. And the American military’s once-singular focus is diffused by the need for reconstruction and a growing fight against the Taliban, the resurgent Afghan Islamic movement that once hosted bin Laden.

American soldiers climbing through the forested mountains of Afghanistan’s Kunar province — where in the 1980s bin Laden fought in the U.S.-backed jihad against the Soviets — still hope to catch or kill him. But they say bolstering the Afghan government is their primary mission now, amid the worst upsurge in Taliban attacks in five years.

“It is like chasing ghosts up there,” said Sgt. George Williams, 37, of Watertown, N.Y., part of the Army’s 10th Mountain Division pushing into untamed territory along the border with Pakistan. “Osama bin Laden is always going to be a target of ours as long as he is out there, but there are other missions: to rebuild Afghanistan and attack the militants still here.”

The top leaders of al-Qaida remain free despite more than 100,000 U.S., Afghan and Pakistani forces at the frontier. High-tech listening posts, satellite imagery, unmanned spy planes — not to mention a $25 million bounty on each man from the U.S. government — all aid the hunt.

Yet both bin Laden and al-Zawahri are communicating to the outside world, posting messages on Islamic Web sites to inspire further attacks on the West. Although the al-Qaida leaders are too isolated to run directly a terrorist operation like Sept. 11, Pakistan says the latest alleged plot, to bomb U.S.-bound jetliners from Britain, may have been blessed by al-Zawahri.

The frustrating campaign has frayed critical cooperation between Afghanistan and Pakistan, neighbors separated by an ill-defined frontier and a history of mutual suspicion.

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.”