CIA Director Leon Panetta, seen during a February news conference, said Sunday there has been little new intelligence about Osama bin Laden in years. (J. Scott Applewhite/Associated Press)

CIA Director Leon Panetta says al-Qaeda is probably at its weakest since the Sept. 11 attacks because of U.S.-led strikes, with only 50 to 100 militants operating inside Afghanistan and the rest hiding in Pakistan's mountainous western border region.

Panetta said Sunday the U.S. hasn't had good intelligence on Osama bin Laden's whereabouts for years and that the terrorist network is finding smarter ways to try to attack the United States.

Of greatest concern, he said, is al-Qaeda's reliance on operatives without previous records or those living in the U.S.

"We are engaged in the most aggressive operations in the history of the CIA in that part of the world, and the result is that we are disrupting their leadership," Panetta told ABC television's This Week.

The rare assessment from the U.S. spy chief comes as President Barack Obama builds up U.S. forces in Afghanistan to prop up the government and prevent al-Qaeda from returning. About 98,000 U.S. troops will be in Afghanistan by fall.

Panetta initially said in the interview that the Taliban leadership was at its weakest point since the attacks of Sept. 11, 2001, when it escaped from Afghanistan into Pakistan. He later corrected himself to say he was talking about al-Qaeda.

On bin Laden, Panetta said he was hiding amid Pakistan's rough terrain with "tremendous security around him."

"If we keep that pressure on, we think ultimately we can flush out bin Laden" and other al-Qaeda leaders, he said.

Good intelligence on bin Laden's location "almost goes back, you know, to the early 2000s. … Since then, it's been very difficult to get any intelligence on his exact location," Panetta said.

Drone strikes defended

Panetta defended CIA drone strikes in the region, saying that claims they violate international law are "dead wrong."

"We have a duty, we have a responsibility, to defend this country so that al-Qaeda never conducts that kind of attack again," he said.

Meanwhile, the chairman of the Senate Armed Services Committee suggested that the U.S.-led operation in the Taliban southern stronghold of Kandahar shouldn't move forward until more Afghan security forces can move into the city.

Senator Carl Levin said there are fewer than 9,000 Afghan troops operating in and around Kandahar as the U.S. begins building up its own forces in the region to try to drive away the Taliban.

While Levin suggested the U.S. delay operations, he insisted that the Obama administration stick with its plan to begin pulling troops from Afghanistan by the middle of next year. Levin told CBS television's Face the Nation that it's up to the Afghans to take control of their country.

U.S. commanders had hoped to finish the Kandahar operation in August, but have now acknowledged it will continue into the fall, in part because of public opposition to the increased military activity.