Eight people have died after a civilian-contracted aircraft crashed at a remote United States Air Force facility in southwestern Alaska, military authorities said on Thursday.

The aircraft went down at the airport serving the long-range radar installation at Cape Newenham, according to the Alaskan Command.

Emergency responders who reached the crash site confirmed that all eight people on board were killed, the military said in a statement.

Authorities have not released the identities or nationalities of the victims, pending notification of their families.

The military also did not disclose the purpose of the flight or why the passengers and crew were at the radar facility, which monitors aircraft operating within Alaskan airspace.

An Alaskan Command spokesperson said an investigation had been launched to determine the cause of the crash and establish the circumstances surrounding the incident.

“This is a devastating loss for our military family and the communities we serve,” said Lieutenant General Robert Davis, head of Alaskan Command.

“These individuals were dedicated professionals carrying out a vital mission in a demanding environment,” Davis added.

Investigators are expected to examine the aircraft, flight operations and other factors as efforts continue to determine what caused the fatal crash.