Al-Qaeda's number two Atiyah abd al-Rahman has been killed in Pakistan, the United States said, claiming another "tremendous" blow to the group following the death of Osama bin Laden.
News of Rahman's demise comes as the US gears up to mark the 10th anniversary of Al-Qaeda's most spectacular attack, on September 11, 2001 on landmarks in Washington and New York, which killed nearly 3,000 people.
Rahman, a Libyan, was killed in the northwest tribal Waziristan area on August 22 after being heavily involved in directing operations for Al-Qaeda, a senior US official said, without divulging the circumstances of his death.
However, local officials in the region told AFP last week that a US drone strike on August 22 on a vehicle in North Waziristan killed at least four militants. It was not clear if the two incidents were connected.
The senior US official, speaking on condition of anonymity, said the death of Rahman would be deeply felt by Al-Qaeda because the group's new leader Ayman al-Zawahiri had relied on him since US Navy Seals killed bin Laden on May 2.
Bin Laden also died in Pakistan, in a sprawling house he was holed up in close to a military academy.
The death of Rahman, who had a $1-million bounty on his head and was said to be an explosives expert, represented "a tremendous loss for Al-Qaeda", the senior official said.
"The trove of materials from bin Laden's compound showed clearly that (Rahman) was deeply involved in directing Al-Qaeda's operations even before the raid," the official said.
"He had multiple responsibilities in the organization and will be very difficult to replace."
Details about Rahman are sketchy and he is not nearly as high profile as bin Laden or Zawahiri.
According to US authorities, Rahman, who was in his late thirties, was appointed personally by bin Laden and was Al-Qaeda's emissary in Iran, recruiting and facilitating talks with other Islamic groups to operate under Al-Qaeda.
He joined bin Laden in Afghanistan as a teenager in the 1980s to fight the Soviet Union.
Rahman's death represents another success for President Barack Obama's intensified and often clandestine operations against Al-Qaeda, particularly in the northwestern tribal regions in Pakistan which Washington says is the group's lair.
In his weekly radio and Internet address on Saturday, Obama called on Americans to recreate the national unity that emerged after the September 11 attacks, and noted that "We're taking the fight to Al-Qaeda."
Another senior US official said "news of (Rahman's) demise underscores what (Defense Secretary) 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.
"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," the official stressed.
The Washington Post cited unnamed officials in July as saying that evidence taken from bin Laden's compound suggested the Al-Qaeda founder was concerned about the impact drone attacks were having on his organization when he died.
Washington has called Pakistan's semi-autonomous tribal region where Rahman died the global headquarters of Al-Qaeda, where Taliban and other Al-Qaeda-linked networks plot attacks on NATO forces in Afghanistan.
Bin Laden was killed in his compound in Abbottabad in a daring raid by US special forces soldiers deep into Pakistan, and the soldiers seized large amounts of intelligence about the group's operations.
In July, Panetta said that the "strategic defeat" of Al-Qaeda was "within reach" and that 10-20 key operatives had been targeted in Pakistan, Yemen, Somalia and north Africa.