The incident, which killed three detectives at a police training facility, is the deadliest law enforcement-related explosion in Southern California in nearly 40 years.

LOS ANGELES, July 18 (Xinhua) -- Three detectives were killed Friday morning in an explosion at a police training facility in Southern California, authorities confirmed.

The Los Angeles County Sheriff's Department referred to the explosion on the social media platform X as a "critical workplace incident," which occurred shortly after 7:30 a.m. local time (1430 GMT) at the Biscailuz Center Academy Training in East Los Angeles.

"There were three department member fatalities," the department said, adding that homicide detectives are investigating the scene.

Local KABC-TV reported that the victims were handling some kind of explosives when the blast occurred, 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 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 county sheriff's department through this "horrific incident" in Monterey Park. The Los Angeles 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 Biscailuz Center Academy Training is home to the sheriff's department's special enforcement units and bomb squad, according to local media.

The county sheriff's department on Friday identified the three deputies killed in the line of duty as detectives Joshua Kelley-Eklund, Victor Lemus and William Osborn, all from the Special Enforcement Bureau's Arson Explosives Detail.

Sheriff Robert Luna praised the fallen officers, noting their combined 74 years of service. "There are no words to express the pain and sorrow we feel," Luna said. "These heroes represented the best of our Department, exemplifying courage, integrity and selfless service. This is not only a heartbreaking loss for their families but for all of us."

Luna noted that the incident marks the department's largest loss of life since 1857.

The incident is the deadliest law enforcement-related explosion in Southern California in nearly 40 years, NBC News reported.

The exact cause of the explosion remains under investigation.