Two soldiers were killed and six others were injured in an accident involving a military vehicle and a troop formation at Fort Jackson, South Carolina, officials said late Friday.

Two of the six injured soldiers are in critical condition, officials said.

No additional information was available Friday evening.

The names of the soldiers are not being released until their families are notified.

“Our hearts and prayers go out to the families of the soldiers we lost today and to the families of the injured,” said Maj. Gen. Pete Johnson, commander of U.S. Army Training Center and Fort Jackson, in a statement. “They represent the best of our nation, and we will endeavor to support all those affected through this difficult time.”

The incident is under investigation.