Al-Qaida's second-in-command, Atiyah Abd al-Rahman, has been killed in a drone attack  in Pakistan  , delivering another big blow to a terrorist group that the U.S. believes to be on the verge of defeat, US officials said on Saturday.

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.