LOS ANGELES—A U.S. Marine died during a training exercise Wednesday at Camp Pendleton in Southern California, military officials said.

The Marine died of injuries sustained in a “tactical vehicle mishap” in the afternoon, the I Marine Expeditionary Force said in a statement.

The Marine’s name was not released, and the cause of the incident was under investigation. Officials said the death was not related to Steel Knight, an annual, large-scale training exercise that began Monday on the base.

No further details were given.

The I Marine Expeditionary Force is the largest of the three Marine expeditionary forces and is located on the coast in San Diego County.