Washington - Osama bin Laden has grown more isolated from al-Qaeda's operatives, but the terrorist network has rebuilt itself in Pakistan's tribal region and remains the single greatest US security threat, the central intelligence director said Thursday.

"Today virtually every major terrorist threat that my agency is aware of has threads back to the tribal areas," CIA Director Michael Hayden said in a speech in Washington.

Al-Qaeda has come under increasing pressure in the tribal region in the last year, which has made it more difficult to operate because of crackdowns by the Pakistani military, Hayden said.

"In the past year alone a number of al-Qaeda leaders who have sought refuge in the tribal areas have died," Hayden said.

The presence of al-Qaeda and Taliban militants in the region along the Afghan border has been a source of tension between Washington and Islamabad. The militants use the rugged terrain to launch cross- border attacks against US and NATO forces in Afghanistan.

The Pakistanis have complained about covert US military operations inside the tribal region and airstrikes by unmanned plans against al- Qaeda and Taliban targets. The US government has not publicly acknowledged the strikes.

Hayden said that al-Qaeda in Iraq has suffered major defeats but predicted but predicted that the terrorist network will have a residual, "smoldering" presence that still poses a threat to the stability of the government.

"This is going to go for a long time before it's just out all together," Hayden said.

He would not comment on whether he will stay on as CIA chief after president-elect Barack Obama takes office in January, but it has been reported that the next president wants to replace the heads of all of the US intelligence agencies. Hayden said he would consider any offers by an Obama administration to stay on the job.