SAN CLEMENTE, Calif. >> Five juveniles have been arrested on suspicion of being involved in the beating of three Marines by a large group of youths on a Southern California pier, authorities said.

The assault happened shortly before 10 p.m. Friday in the city of San Clemente near Camp Pendleton, a Marine Corps base. Video circulating online showed a melee with the victims, who were not in uniform, on the ground being kicked until a woman and a man broke it up.

Arriving deputies initially found two victims but then determined a third Marine was also assaulted, the Orange County Sheriff’s Department said in a statement Tuesday.

Firefighters provided medical aid to the Marines, who declined to be taken to a hospital.

Four boys and one girl were arrested Tuesday and booked for investigation of assault with a deadly weapon, the statement said. Their ages were not specified.

A motive for the attack was not immediately known.

Sheriff’s Sgt. Mike Woodruff said today that investigators were still looking into what led to the incident. One account, that had not yet been confirmed, is that members of the group were setting off fireworks and the Marines tried to intervene to stop them, he said.

Woodruff said there was an “undetermined amount of remaining suspects.”

“With approximately 30-plus individuals and the Marines getting engulfed, the investigators have to review all camera evidence available to determine who did what,” he said.