Los Angeles schools were closed on Tuesday after the district received an electronic threat to many schools, school and police officials said.
Los Angeles police and the FBI were notified of the threat, which is being investigated, officials said.
The electronic threat came via a message, Ramon Cortines, the superintendent of Los Angeles schools, said.
Officials said they were not aware of any other threats.
"In an abundance of caution as superintendent, Cortines has indicated we have decided to close our schools today until we can be actually certain that our schools are deemed safe," Los Angeles School Police Chief Steven Zipperman said.
"We need the cooperation of the whole of Los Angeles today," the school board president said.
Parents were asked not to bring their students to school.
A statement will be issued later Tuesday, Cortines said.
The second largest in the United States, the Los Angeles Unified School District has more than 640,000 students in kindergarten through 12th grade at over 900 schools and 187 public charter schools
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