One official said al-Masri, was linked to the July 7, 2005, attacks against the London transit system.
Al-Masri is believed to have died of hepatitis in late 2007 in Pakistan's lawless tribal area bordering Afghanistan, a second counterterror official said. They spoke on condition of anonymity because of the sensitivity of the matter.
Al-Masri was a senior operational planner for bin Laden and one of the planners behind the London subway suicide attacks in 2005 and the failed plot to explode U.S.-bound airliners in 2006. Most recently he was working to train suicide bombers in Pakistan, CBS News reports.
Al-Masri planned the disrupted 2006 attacks in which as many as 10 passenger jets bound for the United States were supposed to have been blown up over the Atlantic simultaneously with liquid explosives. British authorities arrested 24 suspects in August 2006 after almost a year's surveillance. The suspects planned to smuggle bombs and detonators disguised as drinks and electronic devices onto the planes in their carryon baggage.
The plot caused the United States and Britian to adopt tougher security measures for airline passengers. The United States limited the amount of liquids and gels that could be carried aboard. The British for a time banned almost all carry-ons.
Al-Masri also is believed to have been behind the successful London transit attacks. Those attacks occurred during the morning rush hour in London, when three bombs exploded simultaneously on the London Underground. A fourth bomb exploded an hour later on a bus. The attack killed 52 and injured 700. Four suicide bombers also died.
Little else is known publicly about al-Masri. The U.S. National Counterterrorism Center does not even list him in its profiles of known and most-wanted terrorists.
The Los Angeles Times reported April 2 that, according to European documents, al-Masri is in his mid-40s. He fought in Bosnia in the early 1990s and was wounded in Chechnya before going to Afghanistan in 2000. He fled into Pakistan in late 2001 with other al Qaeda leaders, including Osama bin Laden.
In Pakistan, army spokesman Maj. Gen. Athar Abbas said he had no information about the death of al-Masri. Several Pakistani intelligence officials contacted by The Associated Press had no immediate comment.
Based in the mountainous Afghan province of Kunar, al-Masri was believed to have been in charge of planning attacks on U.S.-led coalition forces in the volatile east region of the country. Violence in southern and eastern Afghanistan spiked last year, killing about 1,600 people. A surge in suicide attacks, a change of tactics by the militants, caused much of the mayhem. The Pakistani government originally had believed al-Masri was killed a CIA Predator strike in 2006.