The number two leader of al Qaeda, Atiyah abd al-Rahman, was killed on August 22 in Pakistan, a senior U.S. official told Reuters on Saturday.
The official did not say how Rahman was killed, but said it happened in Waziristan, northwest Pakistan.
The death, coming soon after the May killing of al Qaeda leader Osama bin Laden, was a huge blow to the extremist organization, the U.S. official said.
"Atiyah's death is a tremendous loss for al Qaeda, because (Ayman al-Zawahri) was relying heavily on him to help guide and run the organization, especially since Bin Laden's death," the official said. Zawahri replaced bin Laden as the leader of al Qaeda after bin Laden was killed, also in Pakistan.
"The trove of materials from Bin Laden's compound showed clearly that Atiyah was deeply involved in directing al Qaeda's operations even before the raid. He had multiple responsibilities in the organization and will be very difficult to replace," the U.S. official said.
U.S. Defense Secretary Leon Panetta said last month on a visit to Afghanistan that he believed the strategic defeat of al Qaeda was within reach if the United States could kill or capture up to 20 remaining leaders of the core group and its affiliates.
"We're within reach of strategically defeating al Qaeda and I'm hoping to be able to focus on that, working obviously with my prior agency as well," said Panetta, who ran the CIA until the end of June.