WASHINGTON--A U.S. drone strike in Pakistan last week appears to have killed a top al Qaeda planner who Washington believes helped organize December's deadly suicide bombing at a CIA base in Afghanistan, U.S. officials said on Wednesday.

The CIA has stepped up the intensity of unmanned aerial drone attacks and intelligence-gathering operations in Pakistan since the Dec. 30 bombing, which killed seven of the spy agency's employees at a heavily fortified U.S. base in the eastern Afghan province of Khost.

"We have indications that Hussein al-Yemeni--an important al-Qaeda planner and facilitator based in the tribal areas of Pakistan--was killed last week," a U.S. counterterrorism official said. "He's thought to have played a key role in the attack on December 30th at Khost."

The Khost bombing, the second-most deadly in CIA history, was carried out by a double agent linked to al Qaeda who was recruited by Jordanian intelligence. U.S. intelligence officials have vowed to avenge the attack.

CIA Director Leon Panetta, in an interview with the Washington Post published on its website on Wednesday, said attacks against al Qaeda in Pakistan's tribal regions appear to have driven Osama bin Laden and other leaders deeper into hiding, leaving the organization incapable of planning sophisticated operations.

Al Qaeda's disarray was so profound that one of its lieutenants, in an intercepted message, pleaded to bin Laden to come to the group's rescue and provide some leadership, Panetta told the newspaper. "It's pretty clear from all the intelligence we are getting that they are having a very difficult time putting together any kind of command and control, that they are scrambling. And that we really do have them on the run," he said.

Other U.S. intelligence officials have warned recently of a continuing threat from al Qaeda, which carried out the Sept. 11 attacks against the United States in 2001, and its affiliates.