WASHINGTON: The United States does not know where Al-Qaeda leader Osama Bin Laden is and has lacked reliable information on his whereabouts for years, US Defense Secretary Robert Gates has said.

The revelation from Gates, speaking in an interview with the ABC News "This Week" program to be aired Sunday, comes days after US President Barack Obama announced he would send 30,000 more troops to Afghanistan.

Asked if Pakistan was doing enough to apprehend Bin Laden, Gates answered: "Well, we don't know for a fact where Osama bin Laden is. If we did, we'd go get him."

Referring to the last time US intelligence had a fix on Bin Laden's whereabouts, Gates said: "I think it's been years."

Bin Laden is believed to have escaped from Afghanistan into Pakistan in late 2001.

In excerpts of the interview released ahead of the broadcast, Gates also could not confirm reports about a detainee in Pakistan who claimed he had information on where Bin Laden was earlier this year.

Part of the United States' reason for going to war more than eight years ago in the wake of the September 11 attacks was to kill or capture Bin Laden.

The Al-Qaeda leader is seen as the chief mastermind of the 2001 attacks in the United States that killed nearly 3,000 people.

Immediately after the attacks, US government officials named Bin Laden and the Al-Qaeda network as the prime suspects and offered a reward of 25 million dollars for information leading to his capture or death.

In 2007, this figure was doubled to 50 million dollars. But so far, the Al-Qaeda founder has eluded capture.

A US Senate report released last week said Bin Laden was "within the grasp" of US forces in late 2001 but escaped because then-defense secretary Donald Rumsfeld rejected calls for reinforcements.

The hard-hitting study points the finger directly at Rumsfeld for turning down requests for reinforcements as Bin Laden was trapped in December 2001 in caves and tunnels in a mountainous area of eastern Afghanistan known as Tora Bora.

"The vast array of American military power, from sniper teams to the most mobile divisions of the marine corps and the army, was kept on the sidelines," the report says.

"Instead, the US command chose to rely on airstrikes and untrained Afghan militias to attack Bin Laden and on Pakistan's loosely organized Frontier Corps to seal his escape routes."

The report commissioned by Senator John Kerry, chairman of the Senate Foreign Relations Committee, says Bin Laden expected to die and had even written a will.

"But the Al-Qaeda leader would live to fight another day. Fewer than 100 American commandos were on the scene with their Afghan allies and calls for reinforcements to launch an assault were rejected.

"Requests were also turned down for US troops to block the mountain paths leading to sanctuary a few miles away in Pakistan.

"The decision not to deploy American forces to go after Bin Laden or block his escape was made by Secretary of Defense Donald Rumsfeld and his top commander, General Tommy Franks," the report says.

Kerry points out at the beginning of the report that when the United States went to war less than one month after the September 11 attacks, the mission was clear: to destroy Al-Qaeda and kill or capture Bin Laden.