|FBI agents had been in touch with Mohamud for months, pretending to be accomplices in the Portland plot
A suspected arson attack has destroyed part of a mosque attended by a US-Somali man accused of plotting a car bomb attack on a Christmas ceremony in the US state of Oregon, investigators have said.
One room in the Corvallis Mosque was gutted in the blaze on Sunday while neighbouring rooms suffered smoke damage, according to the town's fire department.
Officials said there were no injuries in the blaze, which was extinguished within 10 minutes.
"We do have evidence that it was arson," Carla Pusateri of Corvallis Fire Department, said.
The fire occurred less than two days after Mohamed Osman Mohamud, who had attended prayers in the mosque, was arrested while attempting to detonate what he thought was a car bomb at a crowded Christmas tree lighting ceremony in Portland.
In what turned out to be a sting operation by the FBI, Mohamud tried to remotely detonate a fake device supplied by undercover agents who had contacted Mohamud months before and pretended to be accomplices in the plot.
The 19-year-old took classes at Oregon State University in Corvallis, about 130km south of Portland, and the imam at Salman Alfarisi Islamic Centre, where the mosque was related, had previously told local television that Mohamud "occasionally" attended prayers there.
The Federal Bureau of Investigation offered up to $10,000 for information leading to a conviction in the arson case, saying it would not tolerate attacks on the Muslim community.
"This is a big, dangerous mess," Imam Mikal Shabazz, president of the Oregon Islamic Chaplains Organisation and a prominent Muslim activist in Portland, said on Sunday as he learned of the mosque fire.
Shabazz said he had just spoken with an African-American Muslim woman who was verbally attacked by a young man in southwest Portland before others intervened in her defence.
Sam Adams, Portland's mayor, said late on Sunday that he had increased security at city mosques,
Mohamud was due to appear in court on Monday, facing a maximum sentence of life in prison and a $250,000 fine if convicted of the charge of attempting to use a weapon of mass destruction.
A US government complaint quoted him praising the 9/11 attacks on the US and expressing a desire to see "body parts and blood" in Portland.