Reclusive North Korea is to cut the last channel of communications with the South because war could break out at "any moment", has said, days after warning the United States and South Korea of a nuclear attack.

The move is the latest in a series of threats from North Korea in response to new United Nations sanctions imposed after its third nuclear test in February and to "hostile" military drills.

The North has already stopped responding to calls on the hotline to the US military that supervises the heavily-armed demilitarised zone and the Red Cross line that has been used by the governments of both sides.

"Under the situation where a war may break out at any moment, there is no need to keep north-south military communications," a North news agency quoted a military spokesman as saying.