A South Korean Army AH-1S Cobra attack helicopter crashed on Monday during a training flight in the northern county of Gapyeong, killing both crew members on board, the country’s military said.

The helicopter went down shortly after 11am for reasons that remain unclear, it said in a statement.

The two crew members were evacuated to nearby hospitals but were later pronounced dead.

The Army has suspended operations of all AH-1S helicopters following the accident and set up an emergency response team to investigate the cause of the crash.

The training involved practising emergency landing procedures without shutting down the engine, according to the military.