"The cause of the explosion and what the soldiers were doing at that exact time of the explosion are still the subject of investigation," the Army said in a release.

Staff Sgt. Oscar Rodriguez, 27, a native of Beeville, Texas, was killed in the training accident.

Rodriguez was assigned to the 25th Infantry Division's 1st Battalion, 14th Infantry Regiment. Although 7,000 Schofield Barracks soldiers are preparing for a summer deployment to Iraq, 1-14 is not among those with deployment orders, an Army official said.

Rodriguez was killed and the other soldiers were injured during a live-fire training exercise, the Army said.

The Hawai'i County Fire Department previously had said all "sustained blast trauma due to accidental munitions malfunction."

Today's Army release for the first time identified the munition involved in the accident.

An Army Black Hawk helicopter took Rodriguez to Hilo Medical Center, where he was pronounced dead. The other soldiers were also taken to Hilo Medical Center.

The soldier in stable condition has been transferred to Tripler Army Medical Center. The three others, including two in stable condition and one in critical condition, are at The Queen's Medical Center. The two in stable condition are being prepared to be moved to Tripler.

Rodriguez joined the Army in 1996 and was assigned to Schofield in October 2002. He is survived by his wife and son. Yesterday evening, a large American flag hung outside the family's Makakilo townhouse. Friends and a casualty assistance officer were with Rodriguez's wife.

The Army's Combat Readiness Center is heading up an investigation.

The Army suspended live-fire training at Pohakuloa following the accident. Pohakuloa Training Area consists of 109,000 acres near the center of the Big Island. It is used to train ground troops and aircraft units.