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 Waziristan 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.

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.

Rahman's death represents another success for President Barack Obama's intensified and often clandestine operations against al Qaeda.

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, 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.

Copyright AFP (Agence France-Presse), 2011