Khalid Sheik Mohammed, the reputed al Qaeda lieutenant alleged to have organized the Sept. 11, 2001, terrorist attacks on the United States, was arrested by U.S. and Pakistani intelligence agents in the Pakistani city of Rawalpindi.

Mohammed was captured in a predawn raid on a house in Rawalpindi's posh Westridge district. The agents also captured Mustafa Ahmed Hawsawi, a Saudi who allegedly served as paymaster to the Sept. 11 hijackers and has been named in several other federal investigations related to the plot.

Both are jailed at a U.S. detention center at an undisclosed location outside Pakistan.

Mohammed, described by intelligence officials as the principal planner of operations for Osama bin Laden's terrorist network, is believed to be the highest-ranking al Qaeda leader captured in the U.S.-led hunt for members of the organization. Though he has not been charged in the suicide attacks on the World Trade Center and the Pentagon, evidence of his involvement includes a radio interview conducted in December in which Mohammed said he was the mastermind of the attack.

He also has been under indictment since 1996 in a plot to blow up U.S. airliners in flight over the Pacific Ocean.

Hawsawi also has been named in two terrorism-related indictments in this country. He is listed as an unindicted co-conspirator in the case against Zacarias Moussaoui, the only person facing trial in the United States as part of the Sept. 11, 2001, plot. And Hawsawi is named in a false-statements case against Ali S. Marri, a Qatari man who the FBI contends gathered information in his Peoria, Ill., apartment about dangerous chemicals and U.S. infrastructure targets.

-- Kamran Khan

and Susan Schmidt

Khalid Sheik Mohammed is shown, above, shortly after his capture during a raid in Pakistan, and in undated FBI handout photos, bottom left and right.