Feds: Somali-born teen plotted car-bombing in Ore.

Undercover agents in a sting operation stopped a Somali-born teenager from blowing up a van full of explosives at a crowded Christmas tree lighting ceremony in Portland on Friday, federal authorities said.

The explosives were duds supplied by the agents and the public was never in danger, authorities said.

Mohamed Osman Mohamud, 19, was arrested at 5:40 p.m. just after he dialed a cell phone that he thought would detonate the explosives but instead brought federal agents and Portland police swooping down on him.

Yelling "Allahu Akbar!" - Arabic for "God is great!" - Mohamud tried to kick agents and police as they closed in, according to prosecutors.

"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,"

Mohamud, a naturalized U.S. citizen living in Corvallis, was charged with attempted use of a weapon of mass destruction and is scheduled for a court appearance Monday. Few details were available about him late Friday.

There was no word from authorities 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 to The Associated Press and the Oregonian newspaper 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.

Mohamud and the associate used coded language in an e-mail in which the FBI believes Mohamud discussed traveling to Pakistan to prepare for "violent jihad," the documents said.

Last June an FBI agent contacted Mohamud "under the guise of being affiliated with the first associate."

Mohamud and the undercover agent met in Portland on July 30 where the agent and Mohamud "discussed violent jihad," according to the court document.

Prosecutors alleged that Mohamud later mailed bomb components to FBI operatives, who he believed were assembling the device.

"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.

Earlier this month, Mohamud and the agents traveled to the Oregon backcountry and detonated a bomb as a trial run. On the drive back, the undercover officials asked Mohamud if he was capable of looking at the bodies of those killed, according to the federal documents.

"Mohamud responded, `I want whoever is attending that event to leave, to leave either dead or injured."'

He said he wanted to set off explosives at the annual Christmas tree lighting ceremony in Portland's Pioneer Courthouse Square, an event that occurred on Friday.

On Friday, an undercover 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 got out of the van and walked to meet another undercover agent, who drove to Union Station, the Portland train station, where Mohamud was given a cell phone that he thought would blow up the van, according to the complaint.

Mohamud dialed the phone agents had given him, and was told the bomb did not detonate. The undercover agents suggested he get out of the car and try again to improve the signal, when he did, he was arrested, the complaint said.

Omar Jamal, first secretary to the Somali mission to the United Nations, condemned the plot and urged Somalis to cooperate with police and the FBI.

"Talk to them and tell them what you know so we can all be safe," Jamal said.

U.S. authorities have been struggling against a recent spate of terror plans by U.S. citizens or residents.

In the Times Square plot, Faisal Shazhad allegedly tried to set off a car bomb at a bustling street corner. U.S. authorities had no intelligence about Shahzad's plot until the smoking car turned up in Manhattan.

Late last month, Farooque Ahmed, 34, of Virginia was arrested and accused of casing Washington-area subway stations in what he thought was an al-Qaida plot to bomb and kill commuters. Similar to the Portland sting, the bombing plot was a ruse conducted over the past six months by federal officials.

Also in October, a Hawaii man was arrested and accused of making false statements to the FBI about his plans to attend terrorist training in Pakistan.

In August, a Virginia man was caught trying to leave the country to fight with an al-Qaida-affiliated group in Somalia.