Los Angeles shut more than 1,000 public schools on Tuesday over a threatened attack with bombs and assault rifles, sending hundreds of thousands of students home as city authorities fended off criticism that they over reacted to what federal officials later said was most likely a hoax.

The federal officials, who asked not to be identified, echoed an assessment by New York City Police Commissioner William Bratton that the decision in Los Angeles was an "over reaction" and that New York had received a similar threat.

The emailed threat, which authorities said was "routed through Germany" but likely more local in origin, came less than two weeks after a married couple inspired by Islamic State killed 14 people and wounding 22 others at a county office building in San Bernardino, just 60 miles (100 km) away.

"Based on past circumstance, I could not take the chance," Los Angeles School Superintendent Ramon Cortines said at a news conference.

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Los Angeles Mayor Eric Garcetti said he backed the decision by Cortines, and Police Chief Charlie Beck said it shouldn't be second-guessed in the face of a threat that was "very specific to Los Angeles Unified School District campuses."

Beck said the email mentioned assault rifles and machine pistols and implied the use of explosives. He said that officers would search all of the district's campuses.

But the unprecedented move at the second-largest public school system in the United States left some 643,000 students and their families scrambling to make last-minute alternate arrangements and drew wide criticism.

A law enforcement source told Reuters that Los Angeles authorities ordered the closure to allow a full search of about 900 public school facilities without consulting with the Federal Bureau of Investigation, which takes the lead on any potential terrorism investigation. Some public schools in the city remained open as did most private schools.

New York's Bratton said that city's school system, the largest in the United States, had received "almost exactly the same" threat but deemed it non credible.

"L.A. is a huge school system," said Bratton, who had served as police chief in Los Angeles. "To disrupt the daily schedules of half a million school children, their parents, day care, buses based on an anonymous email, without consultation, if in fact, consultation did not occur with law enforcement authorities, I think it was a significant over reaction."

Garcetti denied that assertion, saying that officials had contacted federal law enforcement officials.

Congressman Brad Sherman, a Democrat from California, told CNN that the person who sent the email claimed to be an extremist Muslim, but said the text of the message gave reason to doubt that.

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New York Mayor Bill de Blasio also cited word choices in the note as a reason that city considered the threat a likely hoax, saying that the avowed Muslim who wrote it failed to capitalize "Allah."

Two federal officials, who asked not to be identified, also expressed skepticism to Reuters.

Cortines, in defending his decision to take such a dramatic step, said that the threat stood out from most that the district received in its seriousness and scope, referencing multiple campuses and mentioning backpacks and other packages.

"It is very easy for people to jump to conclusions and I have been around long enough to know that usually what people think in the first few hours is not what plays out in later hours," Garcetti said. "But decisions have to be made in a matter of minutes."

Police Chief Beck said it was "irresponsible" to criticize the decision in the aftermath of the Dec. 2 attack on a regional center in San Bernardino, California, east of Los Angeles.

That massacre and other mass shootings have pushed the issues of militant Islamism and gun violence to the forefront of the U.S. presidential campaign.

Students already at school were sent home, officials said, and families rushed to come up with alternate plans.

"It's disappointing," said Trinity Williams, a high school student who dropped off her younger sister at elementary school, only to find it was closed. The two traveled on to Williams' high school before they realized the whole system was shut down.

"I was supposed to give an essay in class today, and finals are Friday," Williams said. "I can't afford to miss a day."

Lee Stein, parent of a fifth grader at Ivanhoe Elementary School, said he heard about the closure via a news alert to his phone, which he confirmed by calling the principal.

Other parents used social media to vent frustration at having learned about the closures from the news media, rather than directly from the schools.

Ronna Bronstein, who has two sons in grade school, said she was trying to find out more about the incident while shielding her younger child from the news.

"I don't want him to be frightened to go back to school tomorrow," she said.