SEOUL - A South Korean forestry agency helicopter crashed into a reservoir during flight training Monday, killing all three crew, officials said.

The Korea Forest Service said in a statement the chopper smashed into the reservoir in Yeongam, 380 kilometres (235 miles) south of Seoul, with the pilot and two co-pilots found dead in the wreckage.

The cause of the accident was not immediately known, it said.

The Russian-manufactured KA-32 was imported in 1994 largely to fight wildfires.