Al-Qaeda’s second in command was killed last week in Pakistan by a CIA drone strike, according to U.S. officials who said Atiyah Abd al-Rahman’s demise is a significant blow to a terrorist network still reeling from the death of Osama bin Laden.

Rahman was killed Monday in Waziristan, the tribal northwest region of Pakistan, where he presided over the remnants of al-Qaeda and served as a critical link between the lower ranks of the organization and its top leaders, including bin Laden before his death in May.

A senior U.S. administration official called Rahman’s death “a tremendous loss for al-Qaeda” because the group’s new leader, Ayman al-Zawahiri, “was relying heavily on him to help guide and run the organization, especially since bin Laden’s death.”

Rahman was seen as a high-priority target in the CIA drone campaign at a time when U.S. officials have described al-Qaeda as near collapse and have said that a small set of successive blows could all but extinguish the organization behind the Sept. 11, 2001, attacks.

Last month, Defense Secretary Leon E. Panetta said a strategic defeat of al-Qaeda was “within reach” and called for continued efforts to hammer the group’s weakened leadership with a series of attacks.

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

A cache of computer files seized from bin Laden’s compound in Abbottabad, Pakistan, showed that Rahman had emerged as perhaps the most important operational figure in al-Qaeda. A veteran militant who was in regular communication with the al-Qaeda chief, Rahman expressed frustration with the mounting toll of the CIA drone campaign.

In one message, Rahman complained that al-Qaeda’s fighters “were getting killed faster than they could be replaced,” said a U.S. counterterrorism official who, like other sources for this story, spoke on the condition of anonymity, citing secrecy surrounding the drone campaign.

Rahman’s role became even more important after the elevation of Zawahiri, bin Laden’s longtime deputy who has also spent much of the past decade deep in hiding. He is seen as an abrasive and divisive figure who was likely to depend on loyalists, including Rahman, to help keep the network and its increasingly ambitious affiliates from unraveling.

Rahman, a Libyan explosives expert, appears to have met bin Laden when he was still a teenager. He rose to the No. 3 position in the network and was charged with running its financial operations after Saeed al-Masri was killed in a U.S. drone strike in May of last year.

U.S. intelligence officials have regarded Rahman, who was in his early 40s, as an important player in al-Qaeda since at least 2006, when U.S. military officials recovered a long letter that Rahman had sent to al-Qaeda’s chief in Iraq, Abu Musab al-Zarqawi, rebuking the Jordanian for his bloody campaign against Shiites in that country.

Pakistani officials said that they were notified Friday that Rahman had been among those killed in the Monday drone strike and that they had no information about additional casualties.

“There is no question this is a major blow to al-Qaeda,” said a U.S. official familiar with CIA drone operations who portrayed Rahman as an important link to the network’s regional affiliates, including al-Qaeda in the Arabian Peninsula, which is based in Yemen.

“Atiyah was the one affiliates knew and trusted, and he spoke on behalf of both [bin Laden] and Zawahiri,” the official said. “He planned the details of al-Qaeda operations and its propaganda. His combination of background, experience and abilities are unique.”

Rahman was linked with some of al-Qaeda’s boldest operations, including the December 2009 bombing of a CIA compound in Khost, Afghanistan, that left seven agency employees dead. The suicide bomber Humam al-Balawi lured the CIA officers into a trap in part by using a videotape that was purported to be footage of a meeting between Balawi and Rahman. In fact, Rahman was involved in a setup in which he served as bait, helping Balawi secure an invitation to the CIA base at Khost.

A Pakistani intelligence official in the North Waziristan region said four missiles had been fired in the Monday drone strike, two at a vehicle and two at the guest house of a tribal leader. The strikes occurred in Nork, about 12 miles from Miranshah, a town that has been a focal point of the escalating drone campaign for the past two years. Five people were killed in the attack on the vehicle, the Pakistani official said, but it was unknown whether any were killed in the guest house.

A second Pakistani official said that Rahman was “very active and always on the move,” that he had recently been in Mir Ali and had been spotted with both Taliban fighters and Uzbek militants. Rahman sought to cultivate support among locals by providing seed money for shops and businesses, including an auto parts shop, according to a pro-militant tribal elder in Mir Ali.

“If he is lost as reported, this will be a serious blow both in planning and also financially,” the elder said.

Rahman is believed to have served as a liaison between al-Qaeda and Algerian radicals as early as 1993 at a time when militants were waging a civil war against that North African nation. He had previously fought as a guerilla against the Algerian government in the mid-1990s.

But instead of welcoming him, an Algerian rebel network, the Armed Islamic Group, placed Rahman under detention and threatened to execute him for reasons that remain unclear. He and a handful of other Libyan prisoners escaped after five months and fled the country, according to a Libyan political exile familiar with the episode.

Rahman eventually returned to Afghanistan and al-Qaeda’s fold and became one of its leaders after the Sept. 11 attacks, serving as a liaison for al-Qaeda-linked groups in Iraq, Iran and Algeria.

In 2006, the U.S. government posted a $1 million reward for information on Rahman’s whereabouts.

Staff writers William Wan, Joby Warrick, Karen Deyoung and Craig Whitlock in Washington and contributor Haq Nawaz Khan in Peshawar, Pakistan, contributed to this report.