Midhat Mursi al-Sayid Umar has been reported killed before
Reports from Pakistan say a leading al-Qaeda chemical weapons expert, Midhat Mursi al-Sayid Umar, has been killed in a missile strike.
Taleban officials in the tribal area of South Waziristan confirmed to the BBC that he was killed in a missile strike that left at least six people dead.
The US, which has a reward of $5m on his head, said it had no information.
He was wrongly reported to have been killed in 2006 in a strike aimed at al-Qaeda deputy head Ayman al-Zawahiri.
The pre-dawn strike targeted a house near a mosque in the village of Azam Warsak, 20km (12 miles) west of the main town in South Waziristan, Wana.
It was suspected to be a strike by US forces, with residents saying they had heard US drones, but this has not been confirmed.
Pakistani military spokesman Maj Gen Athar Abbas told the AFP news agency it was still awaiting "authentic information" from the area.
Midhat Mursi al-Sayid Umar, 55, also known as Abu Khabab al-Masri, is an Egyptian national.
The US government's Rewards for Justice website says he is "an explosives expert and poisons trainer working on behalf of al-Qaeda".
It says he trained hundreds of militants in chemical and explosives operations at a camp at Derunta in Afghanistan.
The BBC's Syed Shoaib Hasan in Islamabad says the militant was considered part of Osama Bin Laden's inner circle and was said to be in charge of efforts to gain access to, or develop, weapons of mass destruction.
Local residents said the house targeted belonged to a local tribesman and suspected militants used to stay there.
The US is reported to have carried out a number of drone missile attacks in the tribal regions.
Pakistan has complained the attacks could damage bilateral relations.
The latest strike came shortly before Pakistani Prime Minister Yousuf Raza Gilani was due to meet US President George W Bush in Washington.
White House spokeswoman Dana Perino said she had no information about the incident.
In recent months the US and its allies have pledged hundreds of millions of dollars in military and other forms of assistance to help Pakistan's new government tackle militancy in border tribal areas.