NEAR CAMPO, Calif. -- An investigation was under way Friday morning into the fatal shooting of a U.S. Border Patrol agent in Campo, near the Mexican border.

The shooting was reported about 9:15 p.m. Thursday on Shockey Truck Trail southeast of the San Diego Sheriff Department's Campo substation, according to the Sheriff's Department.

A group of border patrol agents came across a group of men near the north end of the border fence, Border Patrol Public Information Officer Daryl Reed said.

As the agents approached, the group of men split up and started running, Reed said.

The agents followed and began a chase. One agent was separated from the group and gunshots were heard, Reed said.

Four engines, paramedics, and a medical helicopter were dispatched to the area, but the agent, who was found with a gunshot wound to the head, was declared dead at the scene, Cal Fire Battalion Chief Nick Schuler said.

The county medical examiner arrived on scene at 3:30 a.m. to retrieve the body of the slain agent, 10News photojournalist Rett Lawrence reported.

FBI Special Agent Darrell Foxworth said his agency is investigating the incident, along with the Sheriff's Department, the Border Patrol and the U.S. Attorney's Office.

The name of the agent was withheld pending family notification.

No information on the shooter was immediately released.