(AP Photo/Brittany Murray, Long Beach Press Telegram)

LONG BEACH, Calif. - A U.S. immigration agent shot and seriously wounded a co-worker during a workplace confrontation before another agent pulled his weapon and shot the gunman to death, the FBI said.

The Immigration and Customs Enforcement agents were shot Thursday evening in the federal building in Long Beach, south of downtown Los Angeles.

The FBI's Steven Martinez described the shootings as a case of "workplace violence involving two federal agents in their office space." He offered no details about what led to the initial shooting.

But the Los Angeles Times, citing multiple law enforcement sources, reported Friday that the initial shots were fired by an agent at his supervisor during an unspecified dispute.

"Another agent, working nearby, intervened and fired his weapon to prevent additional rounds being fired at the victim," said Martinez.

The gunman died at the scene, and the wounded agent was hospitalized. ICE Special Agent in Charge Claude Arnold would only say he was stable.

St. Mary's hospital trauma director James Murray told KCAL-TV the injured agent had multiple gunshot wounds. The victim's vital signs were "good for now," Murray said.

The names of the dead gunman, the victim and the agent who fired the final rounds were not released.