The U.S. believes al-Qaida's No. 2 leader, Attiya Abd al-Rahman, was killed earlier this week in the tribal areas of Pakistan, U.S. officials said Saturday.

Attiyah's death is a tremendous loss for al-Qaida, a senior Obama administration official said. He had multiple responsibilities in the organization and will be very difficult to replace.

The officials said he was killed in Waziristan on Aug. 22, the Wall Street Journal reported. They would not say whether he was killed by a CIA drone strike.

Rahman stepped into a much larger role in the running of the organization after al-Qaida leader Osama bin Laden was killed in a May raid in Pakistan. Rahman, a Libyan national, was the network's former operational leader, before filling al-Qaida's No. 2 slot.

Last month, Defense Secretary Leon Panetta said al-Qaia's defeat was attainable if only the U.S. could stage a string of successful attacks on a 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.

Rahman, believed to be in his mid-30s, was a close confidant of bin Laden, joining him as a teenager in Afghanistan to fight the Soviet Union.