Updated

The Marine Corps is investigating the death of an 18-year-old Marine who died while treading water in a swimming pool during a screening test at Camp Pendleton.

Col. Sean D. Gibson told The Associated Press on Friday that Pfc. Joshua Islam died Monday afternoon while undergoing an initial screening test for an infantry school that involves treading water for 30 minutes in a swimming pool. The test is a precursor to the Marines' physically demanding reconnaissance training.

Officials declined to release details while the investigation to determine the cause of death is ongoing at the base north of San Diego.

Islam was a rifleman from Union County, N.C. He graduated from boot camp at Perris Island three months ago.

Brig. Gen. John Simmons offered his condolences to Islam's family.