So Se Pyong, ambassador of the Democratic People's Republic of Korea (DPRK) to the United Nations in Geneva, also warned that a continued stand-off with Seoul and Washington could lead to confrontation, a "second Korean war".

North Korea said on Saturday it was willing to suspend nuclear tests if the United States agreed to call off annual military drills held jointly with South Korea, but Washington rejected the proposal as a veiled threat.

"The United States is insisting that the nuclear tests and joint military exercise are separate and therefore it is unreasonable to link the moratorium of nuclear tests with the topic of joint military exercises," So told a news conference.

"Moreover, the U.S. and south (Korea) staged joint military exercises in the East Sea of Korea, on the 13th and 14th January, a marine joint military exercise. This is an open challenge to the demand of the DPRK for removing the danger of war and easing the tension on the Korean peninsula," he added.

Pyongyang has often repeated its demand for the allies to end their large-scale defensive drills, which have been carried out for roughly 40 years.

In Washington, U.S. State Department spokeswoman Marie Harf told a briefing on Thursday that the United States "continues to offer the opportunity for meaningful engagement" and improved relations to North Korea if it shows its willingness to meet its international obligations.

"Unfortunately, North Korea continues to rebuff or ignore these offers," Harf said, saying that North Korea instead offers "false choices" like its offer regarding the suspension of U.S. military exercises with South Korea.

"The offer, as I understand it (and) which we see as an implicit threat, is for the U.S. to stop doing something that is routine, that is transparent, that is defensive in nature and that is annual - that we do every year - in exchange for the North Koreans not doing something that is prohibited under multiple U.N. Security Council resolutions and that they are not supposed to be doing. That's really a false choice here. They're not equivalent in any way," Harf said.

NUCLEAR TESTS

North Korea has conducted three nuclear tests, the last in February 2013, and is under U.N. sanctions for defying international warnings not to set off atomic devices in pursuit of a nuclear arsenal, which it calls its "sacred sword".

"About the nuclear test, the policy of my country is that in case they are doing any kind of nuclear war, then we have to make the counter-measures...," So said, without elaborating.

"Otherwise, if there's a standstill and if we are in a state of pause, then there might be another Korean war, the second Korean war in the peninsula."

The Obama administration has blamed North Korea for a crippling cyber attack on Sony Pictures Entertainment (6758.T). North Korea has denied responsibility, though it has described as an "act of war" a Sony comedy, "The Interview", which features a plot to assassinate its leader Kim Jong Un.

So, asked whether he was concerned that the Sony incident could poison relations and impede progress on the nuclear issue, replied: "It depends on the United States. We expressed our position on that. It is up to them."

(Additional reporting by Will Dunham in Washington; Editing by Mark Trevelyan/Hugh Lawson)

www.reuters.com/article/2015/01/15/us-korea-north-envoy-idUSKBN0KO2BS20150115