The 26-year-old is accused of wanting to carry out a violent attack on the popular tourist spot Pier 39
A former US marine has been arrested for telling undercover FBI agents he wanted to attack a popular San Francisco tourist attraction on Christmas Day.
Everitt Aaron Jameson is accused of telling an agent who he believed was associated with the senior leadership of Islamic State that 25 December would be "the perfect day to commit the attack".
The 26-year-old was charged on Friday with attempting to provide material support to a foreign terrorist organisation, and faces 20 years in prison if convicted.
He said he wanted to carry out a violent attack on Pier 39 in San Francisco because it was heavily crowded, according to an FBI affidavit.
Jameson, now a tow-truck driver, said he "did not need an escape plan because he was ready to die".
Pier 39 is one of San Francisco's most popular tourist destinations and is home to numerous restaurants, bars and souvenir shops, as well as the city's aquarium.
Jameson was under surveillance and "the public was never in imminent danger", FBI spokeswoman Katherine Zackel said.
The truck driver posted extremist messages online, with some supporting the Halloween terror attack in New York City when a truck driver rammed into pedestrians, killing eight, the FBI said.
He had offered to use his tow truck for an attack.
The FBI started investigating in mid-September after Jameson liked posts supporting IS.
He "loved" an online post showing Father Christmas threatening to attack New York with a box of dynamite.
On Wednesday agents raided his home where they found a suicide note signed with an Islamic variation of his name with his last will and testament, updated in November.
Fireworks, two rifles and a 9mm handgun were also found.
During the search Jameson "stated his support of ISIS and terrorism and discussed aspects of the plan to carry out an attack, noting that he would be happy if an attack was carried out".
In 2009 he took part in Marine basic recruit training and earned a sharpshooter rifle qualification but was discharged for failing to disclose a history of asthma.
In comments to undercover agents he said: "I have been trained in combat and things of war."
Two years ago Jameson converted to Islam.
Attorney general Jeff Sessions said: "The threat from radical Islamic terrorism is real - and it is serious."
He said federal agents are protecting the nation from "an alleged plot to kill Americans".