WASHINGTON -- Jose Padilla, a U.S. citizen held as a terrorism suspect for two years, sought to blow up apartment buildings in the United States in addition to planning an attack with a "dirty bomb" radiological device, the U.S. government said Tuesday.

Padilla, arrested in May 2000 upon arrival at Chicago's O'Hare Airport, and an accomplice were to locate up to three high-rise apartment buildings that relied on natural gas and rent two apartments in each building, according to documents released Tuesday by the Justice Department.

At a news conference Tuesday, Deputy Attorney General James Comey said Padilla's partner in the attacks was to be Adnan El Shukrijumah, one of seven suspected al-Qaida operatives who the Justice Department cited last week as planning attacks on the United States this summer. Nicknamed "Jafar the pilot," the Saudi native once lived in Florida and has been sought by federal authorities for more than a year.

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According to the documents, the two were to seal all the openings, turn on the gas and set times to detonate the buildings simultaneously at a later time.

Padilla, a former Chicago gang member held on charges of planning to detonate a dirty bomb in the United States, attended a dinner in Pakistan hosted by Khalid Sheikh Mohammed, "the mastermind of the Sept. 11 attacks," the night before departing for the United States, Comey said.

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Al-Qaida officials, including Abu Zubaydah and Mohammed, were skeptical of Padilla's ability to set off a dirty bomb but were very interested in the apartment operation, Comey said. He said Padilla was trained on how to seal the apartments after turning on the gas.

Comey said Padilla was mentored in 2000 and 2001 by Mohammed Attef, the military commander for al-Qaida who was killed in a November 2001 U.S. airstrike. He said Attef, known by experts as the No. 3 figure in al-Qaida at the time, "no doubt saw great value in this American."

With the Justice Department under pressure to explain its indefinite detention of a U.S. citizen as an "enemy combatant," Comey outlined a series of alleged admissions made by Padilla. He asserted that if Padilla had been handled by the more conventional criminal justice system, he could have stayed silent and "would likely have ended up a free man."

The Supreme Court is considering Padilla's challenge to the government's authority to designate U.S. citizens enemy combatants and deny them quick access to lawyers or courts.

Padilla's lawyer, Andrew Patel, said the government once again is saying "bad things about" about Padilla without offering a "forum for him to defend himself." He accused the government of making "an opening statement without a trial."

Comey said an application to be trained at an al-Qaida camp was found by the FBI at a camp in Kandahar in 2002. He said that when the FBI detained him on May 8, 2002, he was carrying $10,000 and a cell phone "given to him by his al-Qaida handlers."