A helicopter crashed in Hawaii on Tuesday morning, killing four people, the Pacific Missile Range Facility (PMRF) confirmed. There were no survivors of the crash, and the victims identities have not been released.

The helicopter was operated by Croman Corporation, a contractor that “provides range support services to PMRF,” the facility said in a statement. The helicopter was supporting a “range training operation” when it crashed north of the missile facility, located near Kekaha on the island of Kauai, just after 10 a.m. local time.

The National Transportation Safety Board identified the helicopter as a Sikorsky S-61N.

The cause of the crash remains under investigation.

The PMRF is a Navy base where the U.S. military tests missile defense technology, according to The Associated Press.

The news comes amid a string of notable helicopter crashes in the U.S. A crash in Miami Beach over the weekend left two people injured. A Huntington Beach police officer was killed in helicopter crash on Saturday in California. Another helicopter crash near an Utah ski resort on Tuesday resulted in no serious injuries.