PORTLAND, Ore. -- Federal agents in a sting operation arresteda Somali teenjust as he tried blowing up a van he believed was loaded with explosives at the crowded Christmas tree lighting ceremony Friday in Portland. The bomb was an elaborate fake supplied by the agents and the public was never in danger, authorities said.

COMPLETE COVERAGE: Portland Terror Plot

Investigators saidMohamed Osman Mohamud, 19, plotted a spectacular show of terrorism for months, saying he didn't mind that children would die if he bombed the crowded ceremony, according to a law-enforcement official and court documents.

Multimedia: Bomb plot timeline

Mohamud was arrested at 5:40 p.m. Friday just after he dialed a cell phone that he thought would set off the blast but instead brought federal agents and police swooping down on him.

Yelling Allahu Akbar! -- Arabic for God is great! -- Mohamud tried to kick agents and police after he was taken into custody, according to prosecutors.

More: FBI says teen acted alone

The threat was very real, said Arthur Balizan, special agent in charge of the FBI in Oregon. Our investigation shows that Mohamud was absolutely committed to carrying out an attack on a very grand scale.

An affidavit in the case revealed frightening details of the plot. In it,Mohamud is quoted as saying he picked Portland because they don't see it as a place where anything would happen. In the affidavit, Mohamud was quotedas saying it's going to be a fireworks show and that his goal in the bomb plot was I want everyone to leave dead or injured.

Read the affidavit

A law enforcement official, who was not authorized to discuss the investigation publicly and spoke on condition of anonymity, told The Associated Press on Saturday that federal agents began investigating the suspect after receiving a tip from someone who was concerned about the teenager.

The FBI affidavit that outlined the investigation alleges that Mohamud planned the attack for months, at one point mailing bomb components to FBI operatives, whom he believed were assembling the device.

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According to the official, Mohamud hatched the plan on his own and without any instruction from a foreign terrorist organization, and he planned the details, including where to park the van for the maximum number of casualties.

The affidavit said Mohamud was warned several times about the seriousness of his plan, that women and children could be killed, and that he could back out, but he told agents: Since I was 15 I thought about all this; and It's gonna be a fireworks show ... a spectacular show.

More: Latest in series of terror plots against U.S.

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.Authorities allowed the plot to proceed in order to build up enough evidence to charge the suspect with attempt.

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Officials didn't say if the suspect had any ties to other Americans recently accused of trying to carry out attacks on U.S. soil, including alleged efforts in May by a Pakistan-born man to set off a car bomb near Times Square or another Pakistan-born Virginia resident accused last month in a bomb plot to kill commuters.

U.S. Attorney Dwight Holton released federal court documents that show the sting operation began in June after an undercover agent learned that Mohamud had been in regular e-mail contact with an unindicted associate in Pakistan's northwest, a frontier region where al-Qaida and Afghanistan's Taliban insurgents are strong.

The two used coded language in which the FBI believes Mohamud discussed traveling to Pakistan to prepare for violent jihad, the documents said.

In June an FBI agent contacted Mohamud under the guise of being affiliated with the suspected terrorist. But the documents did not say how federal officials first became aware of Mohamud.

An undercover agent met with him a month later in Portland, where they discussed violent jihad, according to the court documents.

As a trial run, Mohamud and agents detonated a bomb in Oregon's backcounry earlier this month.

This defendant's chilling determination is a stark reminder that there are people -- even here in Oregon -- who are determined to kill Americans, Holton said. Friday, an agent and Mohamud drove to downtown Portland in a white van that carried six 55-gallon drums with detonation cords and plastic caps, but all of them were inert, the complaint states.

They left the van near the downtown ceremony site and went to a train station where Mohamud was given a cell phone that he thought would blow up the vehicle, according to the complaint. There was no detonation when he dialed, and when he tried again federal agents and police made their move.

The Christmas tree lighting in Pioneer Courthouse Square is a popular annual tradition that draws thousands of onlookers to downtown Portland. This year's tree lighting included performancesby membersofthe internationally acclaimed Pink Martini band.

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On Saturday, Muslim leaders gathered to speak out against the thwarted plot. They praised the actions of Federal investigators, and said that they wanted the city of Portland and the world to know that they stood for peace, not violence.

More: Muslim leaders decry violent plot

Mohamud faces charges that carry a maximum sentence of life in prison.

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