A U.S. Marine Corps pilot based out of Marine Corps Air Station Miramar was killed and another was injured after their helicopter crashed during a training exercise in Imperial County on Thursday, military officials said Friday.

The AH-1Z Viper, a twin-engine attack helicopter that is part of the 3rd Marine Aircraft Wing, went down around 7:05 p.m. in Imperial Gables, a remote area east of Glamis, officials said.

Both pilots in the aircraft were taken to a hospital, but only one survived. Military officials said they would not be releasing the name of the pilot until 24 hours after his family had been notified.

The surviving pilot was taken to Desert Regional Medical Center in Palm Springs and had stable vital signs.

“It is with profound sadness that I share the loss of a Marine from 3rd Marine Aircraft Wing and the ‘Gunfighters’ while conducting a training flight in support of the Marine Corps Weapons and Tactics Instructor Course,” said Maj. Gen. James Wellons, the commanding general for 3rd MAW. “This Marine made the ultimate sacrifice, and we are forever grateful for his selfless commitment and willingness to go into harm’s way.”

“To the family, friends, and loved ones of our fallen Marine, we send our deepest condolences and offer our unwavering support during this time of grief,” Wellons added.

Details about the training exercise and the circumstances of the crash were not released. The cause is under investigation.

Bell AH-1Z Viper has been in use by the Marine Corps since 2011. The helicopter was designed by Bell Helicopter Company.