WASHINGTON — A drone operated by the Central Intelligence Agency killed Al Qaeda’s second-ranking figure in the mountains of Pakistan on Monday, American and Pakistani officials said Saturday, further damaging a terrorism network that appears significantly weakened since the death of Osama bin Laden in May.

An American official said that the drone strike killed Atiyah Abd al-Rahman, a Libyan who in the last year had taken over as Al Qaeda’s top operational planner. Mr. Rahman was in frequent contact with Bin Laden in the months before the terrorist leader was killed on May 2 by a Navy Seals team, intelligence officials have said.

American officials described Mr. Rahman’s death as particularly significant as compared with other high-ranking Qaeda operatives who have been killed, because he was one of a new generation of leaders that the network hoped would assume greater control after Bin Laden’s death.

Thousands of electronic files recovered at Bin Laden’s compound in Abbottabad, Pakistan, revealed that Bin Laden communicated frequently with Mr. Rahman. They also showed that Bin Laden relied on Mr. Rahman to get messages to other Qaeda leaders and to ensure that Bin Laden’s recorded communications were broadcast widely.