An explosion early Friday killed three people and is being investigated at least preliminarily as a possible training accident, according to a law enforcement official briefed on the matter who was not authorized to discuss the matter by name and spoke to The Associated Press on condition of anonymity.

Los Angeles County Fire Department said it responded to calls about a possible explosion around 7:30 a.m.

The Los Angeles County Sheriff’s Department has not confirmed any deaths. Attorney General Pam Bondi said she learned about three deaths from U.S. Attorney Bill Essayli’s office. His office didn’t immediately respond to a request for comment.

California Gov. Gavin Newsom’s office said he’s been briefed on the matter, which occurred at the LA County Sheriff’s Special Operations Bureau in East Los Angeles.

Aerial footage from KABC-TV shows the explosion happened in a parking lot filled with sheriff patrol cars and box trucks.