Al Qaeda's new second-in-command was killed earlier this week in Pakistan, US officials said on Saturday, in a major blow to the group still reeling from the death of Osama bin Laden.

Atiyah abd al-Rahman, a Libyan national, rose to the number two spot when Ayman al-Zawahri took the reins of al Qaeda after bin Laden was killed in May in a US raid in Pakistan.

One US official said Rahman was killed in a strike by an unmanned drone on August 22. He was killed in Waziristan in northwest Pakistan where intelligence officials believe members of Al Qaeda are hiding, other US officials said.

"Atiyah's death is a tremendous loss for al Qaeda, because (Zawahri) was relying heavily on him to help guide and run the organization, especially since bin Laden's death," one US official said.

"The trove of materials from bin Laden's compound showed clearly that Atiyah was deeply involved in directing Qaeda's operations even before the (May) raid. He had multiple responsibilities in the organization and will be very difficult to replace," he said.

US and Pakistani intelligence ties have been strained since the unilateral American strike against bin Laden, and Pakistani intelligence did not confirm Rahman's death.

Sources in Pakistan said four people known to have been killed in a US drone strike on August 22 were local militants and not al Qaeda.

Although most US officials described Rahman as al Qaeda's No.2, one said his rank wasn't as clear, saying he could be considered one of the top three leaders of the organization.

Regardless, Rahman's death, if confirmed, would signal another significant setback for al Qaeda's core group just days before the tenth anniversary of the Sept. 11, 2001 attacks.

In the past decade, al Qaeda's affiliates have become a greater concern, with its Yemen-based off-shoot now seen in Washington as the bigger threat to the US.

Noman Benotman, a former Libyan Islamist and now an analyst with Britain's Quilliam think tank, described Rahman as al Qaeda's "CEO," or chief executive officer.

"This was the one man al Qaeda could not afford to lose," Benotman said.

"In the last two years he successfully, and I think more or less single-handedly, created the dynamics that kept al Qaeda together."

Rahman was originally from the Libya, and his real name was Jamal Ibrahim Ishtawi, Benotman said.

A graduate of the engineering department of Misrata University, he left Libya to go to Afghanistan in 1988 and join the Islamist groups then fighting Soviet occupation, he added.

A US official said Rahman ran daily operations for the group, spoke on behalf of bin Laden and Zawahri and was the one that "affiliates knew and trusted."

"Zawahri needed Atiyah's experience and connections to help manage al Qaeda. Now it will be even harder for him to consolidate control," the US official said.

Zawahri is believed to lack bin Laden's presence or his ability to unite different Arab factions within the group, analysts say.

US Defense Secretary Leon Panetta said last month on a visit to Afghanistan that he believed the strategic defeat of al Qaeda was within reach if the United States could kill or capture up to 20 remaining leaders of the core group and its affiliates.

"News of his demise underscores what Leon Panetta has been saying for some time about al Qaeda: it's important to sustain intense pressure on this group of terrorists and thugs," a third senior US official said.

"Dialing back on al Qaeda leadership in Pakistan, especially while they try to regroup after bin Laden's death, isn't the way to go. For the sake of our national security, they need to be knocked out for good," he added.-Reuters