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 criticise 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 radicalised 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."
More about:
