Two years after Osama bin Laden was named the chief suspect in the September 11 attacks in New York and Washington, the United States, Pakistan and Afghanistan are still hunting the Saudi-born terror mastermind. The search is concentrated along the border between Pakistan and Afghanistan, and the neighbors are feeling the pressure.

Is he alive or dead? A recently released videotape of Osama bin Laden and his top aide, Ayman al-Zawahiri, suggests the target of the world's most extensive manhunt - with a $25 million bounty on his head - is still alive.

Some 60,000 Pakistani troops and thousands of U.S. troops are hunting the leader of al-Qaida, an Islamic militant organization. Many officials suspect he is hiding in the rugged mountains and tribal regions along the porous border between Pakistan and Afghanistan, but no one is sure.

Lieutenant General Ali Mohammad Aurakzai, the commander of Pakistani troops hunting al-Qaida fugitives in the North-West Frontier Province, says there is no evidence suggesting Osama bin Laden is hiding in a specific place, but he says Pakistan and the U.S.-led coalition on the Afghan side are combing the region.

"Definitely we are looking for him [bin Laden] in the entire tribal areas [along the Afghan border]. We don't have any definite information as to where he lives if at all he is in Pakistan. But the possibility cannot be ruled out," he said.

Osama bin Laden allied his al-Qaida group with the Taleban, a fundamentalist Islamic movement that took control of Afghanistan in 1996. Al-Qaida members are thought to have hijacked four U.S. airliners on September 11, 2001, crashing two of them into New York's World Trade Center, and one into the Pentagon building near Washington. The fourth crashed into a farm field.

In response to the attacks, which killed nearly 3,000 people, the United States demanded that the Taleban government hand over Osama bin Laden. When it refused, a U.S.-led coalition invaded and ousted the Taleban, and began its hunt for al-Qaida's leader.

After two years, not even the chairman of the U.S. Joint Chiefs of Staff General Richard Myers is certain where Osama bin Laden might be.

"Nobody knows for sure that Osama bin Laden is alive," said General Myers. "I don't think anybody knows for sure where he is. A lot of people think that most probably it's in the more difficult terrain between Afghanistan and Pakistan where there are people that might be willing to support him. That's a likely location I think but I don't know anybody knows that for sure."

At a news conference in the United States with President Bush in June, Pakistani President Pervez Musharraf said his nation was doing all it can to root out al-Qaida and its supporters.

"This is the first time that the Pakistan Army and our civil armed forces have entered this region [along the Afghan border]," said Pervez Musharraf. "Now if any al-Qaida operative is hiding in this region, we are after them and there is no doubt in my mind that the military will be able to locate any al-Qaida members hiding in this area."

Speaking at the same news conference, President Bush acknowledged Pakistan's crucial role in capturing suspected terrorists.

"Since the September 11 attacks, Pakistan has apprehended more than 500 al-Qaida and Taleban terrorists, thanks to the effective border security measures and law enforcement cooperation throughout the country," he said.

Three of the most important arrests in the U.S.-led war on terrorism have been made in Pakistan. They include al-Qaida's chief of operations, Palestinian Abu Zubaydah, and the terror network's military and planning chief, Khalid Sheikh Mohammad, the alleged mastermind of the September 11 attacks.

But the world's most wanted man, Osama bin Laden, remains at large. And the effort to find him and his supporters is creating friction between Pakistan and Afghanistan.

Many Afghan officials blame Pakistan - once a Taleban ally - for the current resurgence of the Taleban. They say Islamabad is not doing enough to stop Taleban fighters from using Pakistan as a base for attacks in Afghanistan.

The commander of the Pakistani border forces, Lieutenant General Aurakzai, rejects these allegations. He says his country has made great strides in blocking movement of fugitive fighters across the Afghan border.

"We do not claim to have sealed the borders entirely because it's a very long border, it's a porous border," he said. "So there is a possibility of some people cross[ing] or re-crossing. I do not deny that. But to say that they [the Taleban] are using our soil and we close our eyes to any such crossing, I think that is wrong."

U.S. and Afghan officials have called on Pakistan to use a heavier hand in its tribal regions, where the government has historically exercised no control. It is only since the U.S.-led invasion of Afghanistan that Pakistan has entered the region.