All Los Angeles Unified School District campuses were closed on Tuesday morning after a broad bomb threat was made against multiple unspecified schools.

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Officials said during a hastily arranged news conference that the nation’s second largest school district was closed out of "an abundance of caution" after an "electronic threat" was received targeting multiple schools.

Los Angeles Police Department (LAPD) Assistant Chief Jorge Villegas said authorities were in the "process of vetting" the threat to establish "what, if any, validity it has."

“I can’t take a chance,” school district Superintendent Ramon Cortines told reporters.

School facilities were in the process of being searched, he said, adding that schools would remain closed until they had been certified safe.

“I am not taking the chance of bringing children anyplace, into any part of the building, until I know that it is safe,” Cortines said.

The FBI has been notified and is assisting the L.A. school district, a spokeswoman said.

New York City officials said Tuesday that they and several other districts nationwide had received the same anonymous threat but concluded it was a hoax.

New York Police Commissioner William Bratton, a former LAPD chief, said he thought officials in L.A. acted hastily, according to The Associated Press. Mayor Bill de Blasio also said "it's very important not to overreact in situations like this."

"I think the initiator, the instigator of the threat may be a 'Homeland' fan, basically watching 'Homeland' episodes that it mirrors a lot of recent episodes on 'Homeland,'" Bratton said. 

A law enforcement official told the AP that a school board member in L.A. received the threat by email late Monday and that it appeared to come from overseas.

De Blasio described the email threat as "so generic, so outlandish and posed to numerous school districts simultaneously" that officials in New York dismissed it as a hoax.

Details of the threat remain unclear, but the Los Angeles school district’s decision to keep all 640,000 students home is likely to stir new fears of terrorism for an American public that is already on edge over recent killings in San Bernardino, Calif., and Paris.

Those shootings — which are believed to have been either inspired by or directed by the Islamic State in Iraq and Syria — helped prompt the bold decision to close all of the district’s schools, Cortines explained.

“I, as superintendent, am not going to take the chance with a life of a student,” he said.

“Remember, we do get individual threats,” he added. “We do evacuate schools, we do lockdown schools, et cetera, and do not release students until we notify parents.

“What we are doing today is no different than what we always do — except that we are doing this in a mass way.”

President Obama has been informed of the Los Angeles Unified School District's decision to close schools due to the threat, White House press secretary Josh Earnest told reporters Tuesday.

He backed up local officials' decision to keep students at home.

“I’m not going to stand here at this podium and second-guess decisions made by local law enforcement officials," he said. “As these local law enforcement agencies are making these decisions, they do so with the support and assistance of federal agencies”

— This report was last updated at 1:50 p.m..