At least three deputies were killed Friday morning in an explosion at a police training facility in Southern California, according to authorities and local media.

The explosion was reported just before 7:30 a.m. local time (1430 GMT) at the Los Angeles County Sheriff's Department's Biscailuz Center Academy Training, which houses the sheriff's department's special enforcement units and bomb squad, local KABC-TV of the ABC network reported.

The victims were handling some kind of explosives when the blast occurred, said the report, citing preliminary information from sources.

U.S. Attorney General Pamela Bondi described it as a "horrific incident" and confirmed that at least three people died. "Our federal agents are at the scene and we are working to learn more," she wrote on the social media platform X.

California Governor Gavin Newsom was briefed on the explosion, according to a statement from his press office on X.

The Governor's Office of Emergency Services is coordinating with the sheriff's department and offering full state assistance while closely monitoring the situation, the statement said.

Los Angeles Mayor Karen Bass said the city is supporting the L.A. County Sheriff's Department through this "horrific incident" in Monterey Park. L.A. Fire Department, the Bureau of Alcohol, Tobacco, Firearms and Explosives, and the LAPD bomb squad "are assisting at the training facility," Bass said on X.

The specific cause of the explosion is still under investigation.