The explosives, identified as C-4, were being stored at the Marine Corps Air Ground Combat Center Twentynine Palms in San Bernardino County, east of Los Angeles, KGTV-TV of San Diego first reported, citing a source with knowledge of the situation.
"Out of respect for the investigative process, NCIS does not comment on or confirm details relating to ongoing investigations," Naval Criminal Investigative Service (NCIS) spokesman Jeff Houston told Fox News in an email early Friday.
The C-4 disappeared during a long training exercise two weeks earlier and may have been stolen. A reward was being offered for its safe return, the San Diego station reported.
C-4 is a high-powered explosive and one-tenth of the amount stolen could blow up a car, a former bomb technician told KGTV.