VIRGINIA BEACH, Va. (AP) — U.S. service members were injured Thursday when a helicopter they were riding in made a hard landing at a military base in Virginia, U.S. Navy officials said in a statement Friday.

The service members were participating in a routine training at Joint Expeditionary Base Little Creek-Fort Story in Virginia Beach, according to the statement from Capt. Sarah Self-Kyler, director of public affairs for U.S. Fleet Forces Command.

The statement did not say how many service members were involved. The statement also did not detail the extent of their injuries, although they were taken to local medical facilities for treatment.

The joint base is shared between the U.S. Army and Navy and is located at the mouth of the Chesapeake Bay. The base houses and trains some of the nation’s “expeditionary forces,” which are troops mobilized for action. The base is also home to some of the nation’s elite Navy SEAL teams.

The cause of the incident remains under investigation, the U.S. Navy stated.