Los Angeles Beefs Up Metro Security Amid Terror Threat

— -- The city of Los Angeles upped its security presence at transit stations after receiving a terror threat on Monday, officials said.

Law enforcement officials say the threat came from an English speaking male in a foreign country who called into a foreign “public safety hotline” and was deemed credible enough by U.S. foreign partners to be relayed to the FBI.

"This could be real, it could be a hoax, but we must remain calm but vigilant," Los Angeles County Sheriff Jim McDonnell told KABC.

The caller warned of a specific imminent attack, but mistakes limited his credibility, according to law enforcement officials.

Federal and local law enforcement officers were notified very early Monday morning.

The threat was uncorroborated but officials decided to take additional security measures out of an "abundance of caution," law enforcement sources told ABC News.

The caller mentioned a possible attack on Tuesday at the Universal City Red Line station, according to the FBI. The male caller was reporting the threat, not making one himself, officials said.

Commuters at the station on Monday night told KABC they were worried, with one person saying he would not ride the train Tuesday. Others said they would continue their normal routines.

Los Angeles Mayor Eric Garcetti said he was confident in law enforcement's response to the threat and plans to ride the Red Line on Tuesday as a show of support.

ABC News' Tom Liddy contributed to this report.