Three soldiers were killed and three others were injured when the armored vehicle they were riding in rolled over into water during training at Fort Stewart in Georgia.

Three members of the Army's 1st Armored Brigade Combat Team were pronounced dead at Fort Stewart-Hunter Army Airfield, outside of Savannah, after "an early morning training accident" involving a Bradley Fighting Vehicle, the Army said.

"Today is a heartbreaking day for the 3rd Infantry Division, and the entire Fort Stewart-Hunter Army Airfield community," Maj. Gen. Tony Aguto, commanding general of the 3rd Infantry Division, said in a statement. "We are extremely saddened by the loss."

Three other soldiers were injured and were taken to Winn Army Community Hospital for treatment.

"Our hearts and prayers go out to all the families affected by this tragedy," Aguto said.

The Army has yet to release the names of the soldiers involved. Next of kin were being notified, and the incident is under investigation, the Army said.

The Fort Stewart incident comes as more than a dozen U.S. service members have been killed in training exercises in the past year. The death toll has prompted calls from military families and congressional leaders for improved training standards and practices.

In August, the Washington Post reported that fatalities in training exercises outnumber combat deaths 4 to 1. According to the Pentagon, training fatalities are down overall, but at least 15 service members have been killed in the past year. Those fatalities represent an increase from last year.

Among the most recent deaths was in April, when Joshua Braica, 29, a Marines special operator, was killed in an accident at Camp Pendleton in California. A month later, Marine 1st Lt. H. Conor McDowell died in a rollover at the same base. Also in May, Marine Lance Cpl. Hans Sandoval-Pereyra, 21, was killed in Australia. In June, a Humvee crash in Alaska resulted in the death of Army Specialist Marquise Elliott, 25. Staff Sgt. Andrew Michael St. John, 29, was killed in a Humvee rollover in August at Fort Hood in Texas.

The Government Accountability Office is expected to study the series of military fatalities.

The Pentagon has also implemented technical solutions aimed at improving training safety in vehicles, including anti-lock brakes and systems designed to reduce the risk of rollovers.