The bodies of the extremists were taken away by sympathisers and Pakistani authorities are trying to establish their identities through sources in the remote tribal region bordering Afghanistan, the officials told AFP.

Protests erupted across key US ally Pakistan at the weekend after 18 civilians also died in Friday's attack. Islamabad lodged a formal complaint with Washington.

"From local sources we have got the information that around four Al-Qaeda operatives were at a dinner meeting and they were killed," a senior intelligence official said.

"Their bodies were taken away by their accomplices but we are trying to confirm who these operatives were."

One of the dead was said to be Abdur Rehman al-Maghribi, Zawahiri's son-in-law and the head of Al-Qaeda's media operations, the Pakistani daily Dawn said, quoting security sources.

Egyptian Zawahiri was the target of last Friday's attack by Central Intelligence Agency Predator drones but Pakistani officials say he was likely not there at the time.

Another was reportedly Midhat Mursi, 52, also known as Abu Khabab al-Masri, a top Al-Qaeda bomb maker with a five million dollar reward on his head, according to both ABC News and Dawn.

The third was named by Dawn as Abu Obaidah al-Masri, Al-Qaeda's chief of operations for the eastern Afghan province of Kunar, where US and Afghan forces are battling a fierce insurgency.

The fourth militant has not been identified but reports said he may have been an Egyptian national named Mustafa Usman.

"According our reports some foreigners were killed in the incident that occurred in Bajur on January 13. We are investigating their identities," Pakistani Information Minister Sheikh Rashid told AFP.

It is the first time the central government has confirmed that militants died in the attack on Damadola, a village in the Bajur tribal agency. However officials in Bajur said Tuesday that four or five militants were killed.

Pakistani authorities use the term foreigners as official shorthand for Al-Qaeda and Taliban militants thought to have taken refuge in the country after the US-led invasion of Afghanistan in late 2001.

The White House has so far refused to express regret at the attack.

If Mursi has been killed, a US counter-terrorism official said, "that would be a very significant development."

"Obviously a decision along these lines (to launch an attack) is not taken lightly, and you can be assured it was based on very solid information," said the official, who asked not to be identified.

However US officials were unable to confirm the report on Mursi, and appeared to have doubts that he had been definitively identified. "It's an open-ended question on who was at the site of the attack," said another official, who also spoke on condition of anonymity.

A five million dollar reward for Mursi's capture is posted on a State Department list of wanted Al-Qaeda leaders.

It says Mursi operated a training camp in Derunta, Afghanistan where hundreds of mujahideen were trained in the use of poisons and explosives.

He produced training manuals with recipes for crude chemicals and biological weapons, some of which were recovered by US forces in Afghanistan, the posting said.

The US official said Mursi also was associated with videotaped poison gas experiments on dogs in Afghanistan.

Some officials said Abu Obaidah al-Masri could have been a replacement for Al-Qaeda's suspected head of operations Hamza Rabia, whom Pakistan said was killed in December in North Waziristan, another tribal region.

Pakistan said Rabia died when munitions exploded at a house but residents said he died in another suspected US missile strike.

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