Intelligence officials are investigating reports that Al Qaeda's top expert on chemical and biological weapons was among six people killed Monday in a missile strike on Pakistan's tribal areas.
Al Qaeda operative Abu Khabab al-Masri's wife told authorities that her husband died in the attack in South Waziristan, according to a Pakistani military intelligence official. The woman was wounded and hospitalized, he said.
U.S. officials told FOX News that al-Masri was a key trainer and expert in chemical and biological weapons, likely to have operational knowledge of a liquid explosive bomb plot thwarted two years ago. He is considered a "top 10" Al Qaeda target and was part of the original team with Usama Bin Laden who fought against the Soviet invasion of Afghanistan.
The U.S. offers a $5 million reward for information leading to his capture.
Pakistan's army said it had not confirmed the strike killed al-Masri.
Another intelligence official said the strike killed four Egyptians and two Pakistanis. He identified one of the Egyptians as "Abu Khuba," but made clear he was referring to al-Masri.
While the Pentagon declined to respond to questions about possible American involvement in the strike, it followed a series of attacks in recent months on militant leaders in Pakistan's tribal belt that are widely believed to have been conducted by the U.S. military.
The attack came just hours before President Bush met with Pakistan's prime minister, Yousuf Raza Gilani, at the White House amid rising pressure on the Islamabad government to act against Taliban and Al Qaeda strongholds in his country's frontier region.
An American official in Washington expressed cautious optimism about the al-Masri reports.
"There is a real sense that this guy is gone," the official. But he cautioned that there was no material evidence yet to confirm al-Masri's death, such as a photograph of the dead man at the bomb site.
Sources tell FOX News it is probabably only a matter of time before U.S. officials confirm al-Masri's death. They are awaiting further information about the identification of the body, such as DNA evidence or dental records.
One of the Pakistani intelligence officials said al-Masri's body was now in the hands of local militants — complicating efforts to verify its identity.
Al-Masri was previously reported killed in a January 2006 missile strike in the Pakistani tribal region of Bajaur that targeted and missed Al Qaeda's No. 2 leader, Ayman al-Zawahri. Pakistani officials said then that al-Masri was among five al-Qaida militants believed killed in that attack, but bodies were never found.
The U.S. official said al-Masri was not an operations planner for Al Qaeda, but played a crucial role because of his knowledge of explosives and poisons and his death would be a significant blow for the terrorist network.
"Not only does he know about these things, he's trained people on them. He has a role to play, a vital role in external operations. He trains the people who go out to perform them," the official said.
While al-Masri's death is no doubt significant, in the seven years since 9/11 Al Qaeda has never used chemical weapons. Instead, they have continued to rely on homicide bombers and conventional explosives. Al-Masri's goal was to use chemical weapons or poisons, which up until now has not happened.
Several Pakistani officials told The Associated Press that missiles hit a compound near Azam Warsak, a village about 2 1/2 miles from the Afghan border. Security officials initially described the building as a religious school, but a local administrator said the school closed years ago.
Al-Masri had been living in that area for some time training suicide bombers and rigging cars with explosives for attacks inside Afghanistan, one intelligence official said, adding that al-Masri's wife, daughter and son were all wounded in Monday's attack and were being treated at a private hospital in Wana, the main town in South Waziristan.
A second intelligence official said the government was working to confirm al-Masri's death. "We believe he's the same guy," he said.
Both officials spoke to The Associated Press on condition of anonymity because they were not authorized to comment to journalists.
The Pakistani army's spokesman, Maj. Gen. Athar Abbas, said troops were trying to reach the area to determine what happened.
The Web site of the U.S. government's Rewards for Justice program says al-Masri, 55, ran a terrorist training camp in Afghanistan before the hard-line Taliban regime was ousted in late 2001.
Al-Masri's "whereabouts are unknown at this time, though he may be residing in Pakistan. It is likely that he continues to train Al Qaeda terrorists and other extremists," the Web site says.
Asked if he had any details about Monday's attack, Defense Department spokesman Bryan Whitman said: "We have a very close working relationship with Pakistan. We respect their sovereignty. Pakistan is an ally in the global war on terror. Beyond that, I have nothing specific for you."
The recent missile strikes in the border region have strained Pakistan's relations with Washington, particularly since a new government took power nearly four months ago and sidelined the U.S.-allied President Pervez Musharraf.
Pakistani officials are seeking peace agreements in the border region in hopes of curbing Islamic extremists who have been blamed for a wave of suicide attacks across the country in the past year.
NATO contends the cease-fire deals have allowed militants based in the frontier region to step up attacks in Afghanistan, while U.S. officials warn that Al Qaeda leaders hiding along the border could be plotting another Sept. 11-style attack on the West.
The Associated Press and FOX News' Catherine Herridge contributed to this report.