Al-Qaeda's number two Atiyah abd al-Rahman has been killed in Pakistan, the United States said on Saturday, 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.