North Korea Threatens New Nuclear Test

North Korea has warned it has not ruled out a test of its nuclear deterrent in retaliation for the US conducting "madcap nuclear war" exercises in South Korea this month.

A statement issued via the country's state news agency KCNA said it was unacceptable the UN Security Council condemned North Korea's military exercises while ignoring simultaneous drills by the US.

"It is absolutely intolerable that the UN Security Council - turning a blind eye to the US madcap nuclear war exercises - 'denounced' the Korean People's Army's self-defensive rocket launching drills and called them a 'violation of resolutions' and a 'threat to international peace and security'," the statement said.

The country's foreign ministry added it would respond with an "appropriate step" involving "more diversified nuclear deterrence" used for hitting medium and long-range targets "with a variety of striking power".

Every year the US and South Korea conduct joint battle exercises involving some 12,500 US and as many as 200,000 South Korean troops.

Operation Key Resolve is a computer-simulated drill which plays out war-time scenarios that could result from a North Korean invasion of the South, while Operation Foal Eagle is a two-month air, sea and land field-training exercise.

The annual drills are regularly condemned by the North as preludes to a US invasion, though Washington insists the exercises are defensive.

North Korea conducted its third nuclear test in February 2013 and claims to have made progress securing a functioning atomic arsenal, though experts note it is unlikely the country possesses warheads capable of reaching the US.

Tensions have increased in recent weeks after North Korea tested its medium-range rocket capability by firing two Rodong Missiles into the sea off the east coast last week, a move condemned by the UN Security Council.

It was also reported that a Chinese passenger plane also crossed the path of a ballistic North Korean missile during a test launch.

The China Southern Airlines flight was flying from Narita airport in Tokyo to the northeastern Chinese city of Shenyang as the rocket was in the course of descending, according to South Korea's defence ministry.

It said the civilian plane, which had 220 passengers on board, "passed as the ballistic missile (from North Korea) was in the course of descending".

Qin Gang, a spokesman for the Chinese Foreign Ministry, said China had contacted the North Korean side to convey its deep concern.