The Libyan national had been the network's operational leader before rising to al-Qaida's No. 2 spot after the US killed al-Qaida leader Osama bin Laden during a raid on his Pakistan compound in May.

Defense Secretary Leon Panetta said last month that al-Qaida's defeat was within reach if the US could mount a string of successful attacks on the group's weakened leadership.

"Now is the moment, following what happened with bin Laden, to put maximum pressure on them," Panetta said, "because I do believe that if we continue this effort we can really cripple al-Qaida as a major threat."

Since bin Laden's death, al-Qaida's structure has been unsettled and U.S. officials have hoped to capitalize on that. The more uncertain the leadership, the harder it is for al-Qaida to operate covertly and plan attacks.