The confontation occurred in front of the Federal Building in Westwood Sunday

By Gadi Schwartz and Kelly Goff

Via: NBC Los Angeles

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.

Updates: 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.