The threat of a terror attack against a busy commuter rail station in the Los Angeles area has prompted authorities to increase security throughout the region and urge commuters to report any suspicious behavior they see.

FBI, LAPD and sheriff's department officials said Monday they received a telephone call about an imminent but uncorroborated threat against the Metro Red Line in Universal City. The threat came from overseas through an anonymous phone call to a public safety line, said FBI Assistant Director in Charge Deirdre Fike in a news conference.

The overseas tip line caller indicated that something would occur at the station at Lankershim Boulevard across from Universal Studios on Tuesday, she said.

Law enforcement officials have stepped up security at the station and other transit stations across the area while authorities still worked to determine the credibility of the threat. Orange barriers were installed at the Red Line Universal Station early Tuesday. Armed members of the Los Angeles County Sheriff's Department were at the station, just off the 101 Freeway in the San Fernando Valley.

Mayor Eric Garcetti himself arrived at the Universal City station to ride the red line to Koreatown, telling another rider he didn't think the threat was credible.

Some commuters underwent bag searches before boarding trains.

"We wanted to have an abudance of caution here today," said Garcetti.

The mayor said information about the threat was provided by a man who claimed to know an individual who planned to carry out the attack. Garcetti said Tuesday morning that investigators are still attempting to uncover more details about the threat and determine whether it was credible.

Deirdre Fike, assistant director of the FBI's Los Angeles office, told reporters Monday night the caller threatened to carry out the attack sometime Tuesday at the Los Angeles County Metropolitan Transportation Authority's Universal City rail station, near Universal Studios.

Garcetti urged caution but asked that the public go about their normal day.

More than 145,000 riders use Metro's Red and Purple lines each day, Garcetti said.

Los Angeles County Sheriff Jim McDonnell urged "people to always be vigilant as they go about their daily routine." He said uniformed deputies will have an increased presence at stations, and undercover deputies will also be on the job on the transit system.

LAPD Chief Charlie Beck said the threat was "very specific," targeting the specific station, "but the credibility still needs to be vetted out."

The timing and specificity of the threat also prompted officials to share the information with the public.

Rep. Adam Schiff, the ranking member of the House Permanent Select Committee on Intelligence, said he was briefed by law enforcement Tuesday morning.

"If it turns out to be a hoax like the prior threat against the LAUSD, it will represent another profound example of the extraordinary cost imposed on communities throughout the United States by such actions," Schiff said in a statement.

He was referring to a threat hoax about one year ago that closed all Los Angeles Unified School District schools. The nation's second largest school district was shut down after a threat that mentioned explosives and weapons.

It was later determined the threat and a similar one received by New York schools were hoaxes.

McDonnell urged residents to stay calm but remain vigilant.

"We've been running this to ground all day long," he said. "This could be real, it could be a hoax. But we must remain calm but vigilant. And we're asking the public to take the same precautions they would take on any other day. And we ask that people always be vigilant as they go about their daily routines. As far as actions we're taking, what you don't see is just as important as what you will see. You will see ... an increased uniformed presence especially at transit stations where we also deploy our K-9 explosive detection teams. We'll have undercover operations under way as well.''

Frequent riders of the Red Line shared mixed opinions Monday night.

"I'll come at same time, leave at same time," Armand Montalva said. "I'm sure people say crazy things all the time."

"You could never be too careful. You could never be too safe," Rashad Green said. "I'm definitely gonna do something different tomorrow. Believe that. I will definitely not be taking the Red Line tomorrow."

Officials repeated the mantra, "If you see something, say something," while urging people to go about their lives but to contact authorities if they notice something that doesn't seem right.

Residents can call 877-A-THREAT and officials urged people to download the LAPD's iWatchLA app from the department's website at www.lapdonline.org.