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Somali-born teen plotted car-bombing in Ore.

This image provided by the Multnomah County Sheriff's Office shows Mohamed Osman Mohamud, 19, arrested and charged with attempted use of a weapon of mass destruction. Officials say he tried to detonate a vehicle bomb at Pioneer Courthouse Square during the tree lighting ceremony Friday, Nov. 26, 2010. They said the bomb was a dummy that FBI agents supplied him. (Multnomah County Sheriff's Office)

November 27, 2010 12:00:00 AM PST
A Somali-born teen was arrested after he tried to blow up a car bomb at a crowded Christmas tree lighting ceremony in Portland, Ore.Undercover FBI agents were able to thwart the attack.

The agents sold 19-year-old Mohamed Osman Mohamud fake explosives and set him up on a sting operation.

Mohamud was arrested just after 5:30 p.m. Friday when he tried dialing a cellular phone he thought would set off the explosives.

Instead, the call brought federal agents and police swooping down to arrest him.

The FBI said Mohamud was planning the attack for months, and at one point, he mailed bomb components to FBI operatives whom he believed were assembling the device.

Mohamud, a naturalized U.S. citizen living in Corvallis, was charged with attempted use of a weapon of mass destruction, which carries a maximum sentence of life in prison. A court appearance was set for Monday.

The Associated Press contributed to this report.