A “very specific” threat has been called in from a foreign country against Los Angeles’ Red Line commuter rail system, US police say.
Law enforcement officials alerted the public to the threat at the news conference, saying it had been passed on to the FBI by authorities in another country, where the threat had originated.
“This threat is imminent, … it is very specific,” Los Angeles Police chief Charlie Beck said.
“But the credibility still needs to be vetted.”
Officials did not identify the country where the threat originated.
The male caller, speaking in English, had warned authorities in that country of an attack against a Red Line station across the street from the Universal Studios theme park on Tuesday, Mr Beck said.
The caller did not threaten to carry out the attack but said he was alerting law enforcement. The Red Line runs between downtown Los Angeles and northern neighbourhoods, including Hollywood and North Hollywood, and carries about 145,000 passengers a day as part of the city’s larger transit system.
It does not operate between the hours of 2:00am and 4:00am.
Mr Beck and Los Angeles County Sheriff Jim McDonnell said authorities would step up patrols at the Universal City/Studio City station and elsewhere along the city’s rail lines.
“You will see additional measures but they are out of an abundance of caution,” Mr Beck said.
Mayor Eric Garcetti said he would board the train at the Universal City station himself on Tuesday as a show of confidence.
“Everybody should go about their normal day tomorrow,” Mr Garcetti said.
“People may see heightened security … But don’t let those [additional officers] frighten you.”