LOS ANGELES (AP) — A blast at a Los Angeles County Sheriff's Department training facility killed three members of its arson and explosives unit Friday, marking one of the department's worst losses of life from a single incident, authorities said.

All three were veteran deputies. The department has not said what they were doing at the time or what caused the explosion.

Los Angeles County Sheriff Robert Luna said the arson and explosives team undergoes in-depth training and responds to more than 1,000 calls a year. Those killed were identified Friday evening by the department as Detective Joshua Kelley-Eklund, Detective Victor Lemus and Detective William Osborn. They served 19, 22 and 33 years in the department respectively, Luna said.

"They have years of training," the sheriff said at a news conference. "They are fantastic experts, and unfortunately I lost three of them today."

The explosion was reported about 7:30 a.m. at the Biscailuz Training Facility, according to sheriff's department spokesperson Nicole Nishida.

Officials were exploring whether there may be a connection to the discovery the previous day of "devices" at an apartment complex in Santa Monica, Nishida said, without specifying what sort of devices they were. The three members of the arson and explosives team responded that day to assist local police.

Law enforcement agencies were obtaining a warrant to search the complex for potential explosive material, and police evacuated residents, Nishida said.

Aerial video from KABC-TV showed that the explosion happened in a parking lot filled with sheriff's patrol cars and box trucks. Three covered bodies could be seen near a truck with a ramp attached to a side door. A patrol cruiser parked nearby had its rearview mirror shattered by the blast.

Luna said it took more than four hours to render the scene safe and the deaths were being investigated by the department's homicide detectives, with the assistance of the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives. No one else was injured, he said.

U.S. Attorney General Pam Bondi said in a post on the social platform X that the explosion "appears to be a horrific incident" and federal agents were at the scene to learn more.

"Please pray for the families of the sheriff's deputies killed," Bondi said.

Luna said the deaths marked the department's worst loss of life in a single incident since 1857, when four officers were killed by gunfire.

"I have met with two of three families thus far. Those were extremely challenging conversations," Luna said, his voice breaking.

Arson investigators from the Los Angeles Fire Department and members of the Los Angeles Police Department bomb squad were also assisting the investigation, Los Angeles Mayor Karen Bass said via X.

Gov. Gavin Newsom's office said he was briefed and the Governor's Office of Emergency Services was in contact with the Sheriff's Department and closely monitoring the situation. He later said on X that members of the State Fire Marshal were helping with the investigation at the request of the ATF.

Jason Zabala, a deputy on the sheriff's department SWAT team, said those who died were "the best of the best."

"When you sign up for the job, you know it's going to be a dangerous job," he said, adding that as time passes, "you realize how dangerous it is."

The department held a procession and service for the fallen deputies in the evening.