LOS ANGELES

- The nation's two biggest school systems - New York City and Los Angeles - received threats yesterday of a large-scale jihadi attack with guns and bombs. LA reacted by shutting down the entire district, while New York dismissed the warning as an amateurish hoax and held classes.

It's extremely rare for a major U.S. city to close all its schools because of a threat and it reflected the lingering unease in Southern California following the terrorist attack that killed 14 people at a holiday luncheon two weeks ago in San Bernardino.

In LA, the threat came in the form of an email to a school-board member. Authorities in New York reported receiving the same "generic" email and decided there was no danger to schools. Mayor Bill de Blasio concluded the threat contained "nothing credible."

"It was so outlandish," he said.

New York Police Commissioner William Bratton agreed. Bratton, who was police chief in Los Angeles until 2009, said that it looked as if the sender of the threat had watched a lot of the terrorism drama "Homeland."