Al-Masri is implicated in the 2005 London transportation network bombings, an elaborate plan involving several planes bound for the United States and a botched plot in Denmark last fall.

"He is not at the very top of al-Qaida, but has been part of the core circle for a long time," a British official told The Los Angeles Times Wednesday.

Police uncovered a plot in August 2006 to explode five planes in midair using liquid explosives, which U.S. counter-terrorism officials linked to al-Masri.

Several strikes against targets in the Pakistani tribal area of Waziristan, thought to be an al-Qaida stronghold, aimed at al-Masri, but they missed, officials said.

Al-Masri showed up again in 2007 in Waziristan instructing Pakistanis of Danish origin on how to make bombs and last week, officials charged three suspects with a Danish plot meant to respond to cartoons said to insult the Muslim prophet, Mohammed.

Intelligence officials suspect al-Masri died in an airstrike, but there has been no evidence either with intelligence reports or statements from Islamist groups.

Both sides may avoid publicizing his death, but one senior British intelligence official notes working as an al-Qaida chief is a job with the lowest life expectancy in international politics."