Al Qaeda's operations chief in Pakistan and a top aide are believed to be dead, a US counterterrorism official says.
The men are believed to be Usama al-Kini, described as al-Qaeda's chief of operations in Pakistan, and his lieutenant Sheikh Ahmed Salim Swedan, both Kenyan-born.
The official declined to discuss how or when the men died, other than to say it was in South Waziristan, in Pakistan's border area with Afghanistan.
A suspected US drone strike in South Waziristan killed three foreign fighters on New Year's Day, intelligence agents in Pakistan said at the time.
The CIA, believed to conduct drone strikes in the region, declined to comment. Pakistan has protested against US strikes as a violation of sovereignty, and the United States has refused to confirm them.
"These deaths are a significant near-term degradation of al Qaeda's leadership," the official said.
Usama al-Kini was thought to have been responsible for attacks including the bombing of a Marriott hotel in Islamabad that killed 55 people in September and an unsuccessful attempt to kill former Pakistani Prime Minister Benazir Bhutto, who was later assassinated in a separate attack, the official said.
The two men were on the FBI's list of most wanted terrorism suspects and had been indicted for the 1998 bombings of US embassies in Tanzania and Kenya.