At least 15 soldiers are injured following an explosion in a training exercise at the U.S. Army Special Operations Command Fort Bragg, North Carolina on Thursday morning.

The soldiers were airlifted to nearby Womack Army Medical Center. The cause of the explosion is unclear. The U.S. Army Special Operations Command is investigating the cause of the incident.

“We‘re looking into an incident that occurred today on Fort Bragg,” said Lt. Col. Robert Bockholt, a spokesman for USASOC, as cited by the Army Times.

“It did incur injuries, but the extent of the injuries are yet to be determined,” Bockholt said.

Fort Bragg is the largest military installation in the world, by population, housing more than 50,000 active personnel.

It’s the home of the 82nd Airborne Division along with the U.S. Army Special Operations Command.

On Wednesday there was another incident at a Marines base at Camp Pendleton, California. Some 15 Marines were injured in a vehicle fire, eight of whom were transferred to the burn unit.