NEW YORK -- A former Denver airport shuttle driver admitted Monday to a plot to bomb the New York City subways, saying he was recruited by al-Qaida in Pakistan for a "martyrdom plan" against the United States.

"I would sacrifice myself to bring attention to what the U.S. military was doing to civilians in Afghanistan," Najibullah Zazi, 25, told a federal judge in a Brooklyn courtroom.

The Afghan native pleaded guilty to conspiracy to use weapons of mass destruction, conspiracy to commit murder in a foreign country and providing material support for a terrorist organization. He faces a life prison sentence without parole at a sentencing in June.

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Zazi said he went to Pakistan in 2008 to join the Taliban and fight against the U.S. military but was recruited by the terrorist network and went into a training camp.

He admitted building homemade explosives with beauty supplies purchased in the Denver suburbs and cooked up in a Colorado hotel room, then driving them cross-country to New York City just before the eighth anniversary of the Sept. 11 terror attacks.

Zazi told authorities he disposed of the explosives once arriving in New York.

He said the terrorism plot was aimed at the city subway system but wouldn't name a specific target when asked by U.S. District Judge Raymond Dearie.

Zazi was arrested in the fall after arousing authorities' suspicions by driving cross-country from Denver to New York around the anniversary of the Sept. 11, 2001, attacks.

Law enforcement officials told The Associated Press that the jailed Zazi jailed Zazi recently volunteered information about the bomb plot during a meeting with his attorney and federal prosecutors in Brooklyn. The sit-down, known as a proffer session, typically signals that a defendant has begun cooperating in a bid for a plea deal.

One of the people familiar with the Zazi case told the AP that Zazi decided to offer the information after being warned that his mother could face criminal immigration charges. The officials spoke on condition of anonymity because the investigation is in progress.

Zazi's attorney, William Stampur, would only say after the hearing Monday: "The plea speaks for itself."