Los Angeles schools have been closed due to a threat emailed to the school district, two weeks after the deadly attacks in California.
The shutdown closed more than 1,000 schools attended by 640,000 students across the city and beyond.
A school district spokesman said it involved rucksacks, and they were exercising “an abundance of caution”.
New York City officials said they received a similar threat but it was so “outlandish” they ignored it as a hoax.
Congressman Adam Schiff, the ranking Democrat on the House Intelligence committee, said the Los Angeles email was also deemed a hoax.
New York City Police Commissioner William Bratton said the emailed threat came from overseas, purporting to be from jihadists, but was not considered credible.
He said he thought Los Angeles officials overreacted.
But LA Police Chief Charlie Beck responded by saying it was “irresponsible” to criticize when you didn’t have the responsibility of safeguarding three-quarters of a million lives.
The threat came less than two weeks after 14 people were killed by a radicalized Muslim couple in San Bernardino, 60 miles east of Los Angeles.
“Earlier this morning we did receive an electronic threat that mentions the safety of our schools,” said Steven Zipperman, chief of the Los Angeles school police department.
“We have chosen to close our schools today until we can be absolutely sure that our campuses are safe.” (Foreign)