A U.S. Immigration and Customs Enforcement agent is dead after a workplace dispute erupted into gunfire at the agency’s offices in a California federal building, officials said.

In the incident at the Glenn M. Anderson Federal Building in Long Beach, Calif., an ICE agent allegedly opened fire on a colleague Thursday evening, leaving that colleague hospitalized in stable condition with multiple gunshot wounds, ICE officials told ABC News.

“This situation began with what we can characterize as an incident of workplace violence,” Steven Martinez, assistant director in charge of the FBI’s Los Angeles office, told reporters late Thursday Pacific Time.

However, a third ICE agent evidently intervened by firing at the initial shooter, Martinez said.

“This resulted in the death of the shooter,” Martinez said. “At this time, we believe this was an isolated incident and the shooter was acting alone.”

The intervening ICE agent was unharmed, officials said.