Updated

WASHINGTON -- CIA Director Leon Panetta said Sunday that 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 along Pakistan's mountainous western border.

Panetta said 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's "This Week."

The rare assessment from the nation's spy chief comes as President 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.

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.