Vietnam's military has temporarily grounded Vietnam War-era U.S.-built helicopters after a crash killed four personnel.

The UH-1 "Huey" chopper crashed in farmland on Wednesday soon after taking off from Ho Chi Minh City on a training flight.

Army Deputy Chief of Staff Lt. Gen. Vo Van Tuan said all UH-1 helicopters would be grounded for maintenance checks. He said crew members had found a problem with the control system of the doomed aircraft and had tried unsuccessfully to fix it.

Tuan said the chopper, one of some 50 Hueys originally belonging to American forces but seized by the victorious communists when the war ended in 1975, was overhauled in the United States in 2012. He declined to say how many are still in service.