Four people were arrested at a pro-Israel peace rally in front of the Federal Building in Los Angeles Sunday after pro-Palestinian protesters also turned up and the two sides clashed.

At least one gunshot was fired by a Federal Protective Service officer, the Los Angeles County Sheriff's Office said.

Four men were arrested on suspicion of assault with a deadly weapon, according to the Los Angeles County Sheriff's Department. The weapons were identified by the department as wooden flag poles.

Witnesses in Westwood said the confrontation included a scuffle between men who drove past the protest displaying a Palestinian flag and pro-Israel protesters. A witness captured the confrontation on video (scroll down to view) that shows.the pickup with its windows rolled down and passenger-side door open traveling past a crowd of people.

A man who said he was in the truck said the Palestinian flag was ripped away. When men from the truck attempted to retrieve the flag, there was a confrontation.

As several of the men tried to leave the scene, at least one gunshot was fired at the truck by the FPS officer.

No one was struck by the gunfire.

The shooting will be investigated by the Los Angeles County Sheriff's Department, assisted by the FBI, according to FBI spokeswoman Laura Eimiller.

Editor's Note: Police earlier told NBC4 that a Department of Homeland Security agent had fired at the truck. Police later said that it was an FPS officer that had fired.

NBC4's Toni Guinyard contibuted to this report.