Three Los Angeles County sheriff’s deputies assigned to the arson explosives detail were killed in an explosion at a law enforcement training facility on Friday, the sheriff said.

Three members of the arson and explosives unit of the Los Angeles County Sheriff’s Department were killed Friday in a blast at the department's training facility.

A state official briefed on the incident, who spoke on condition of anonymity because he was not authorized to discuss the investigation, said preliminary information had suggested that the explosion...