A U.S. missile strike in Pakistan killed the number two leader of al Qaeda Monday, dealing another blow to the terrorist group, U.S. and Pakistani officials said.

Atiyah al-Rahman once served as Osama bin Laden's personal emissary. He was killed in the tribal region of Waziristan.

Since bin Laden's death, counterterrorism officials have hoped to capitalize on al Qaeda's unsettled leadership.

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

Al-Rahman was regarded as an instrumental figure in al Qaeda, trusted by bin Laden to oversee the group's daily operations.