Los Angeles public schools reopen Wednesday after an emailed threat caused officials to close the system Tuesday.
Los Angeles Mayor Eric Garcetti said an investigation by the Federal Bureau of Investigation and local police concluded that the threat was not credible.
U.S. Congressman Adam Schiff, who represents parts of the Los Angeles suburbs said on Twitter that the preliminary assessment is that the e-mailed threat was aimed at disrupting schools in large cities.
The message threatened schools with a large-scale attack using assault rifles, machine guns and bombs.
In New York, officials said they received a similar threat and determined it to be a "hoax."
"We will be vigilant. But we are absolutely convinced our schools are safe," New Mayor Bill de Blasio said.
But Los Angeles officials were cautious since the threat came just two weeks after apparent Islamic State sympathizers killed 14 people wounded 22 in the nearby city of San Bernardino.
“It was not to one school, two schools or three schools, it was many schools, not specifically identified, but there were many schools,” school superintendent Ramon Cortines said. “That’s the reason that I took the action that I did.”
Police spent the day searching all 900 Los Angeles area public schools -- the nation's second-largest school system after New York City.