"This is a dangerous act of throwing a wet blanket over the current positive atmosphere of inter-Korean relations ... which could drive again into an extreme phase of confrontation," Han Tae Song, North Korea's Ambassador to the United Nations in Geneva, said.
South Korean President Moon Jae-in said on Monday a thaw in relations between the two Koreas ahead of next month's Winter Olympics presented a "precious chance" for the United States and North Korea to discuss the North's weapons programmes.
North Korea is developing missile and nuclear technology amid regular threats to destroy the United States and Japan and in defiance of U.N. Security Council resolutions.
Han, addressing the U.N.-sponsored Conference on Disarmament, said nuclear tests last year had allowed his country to "perfect a national nuclear force" in a transparent manner.
"Thus DPRK (North Korea) at last came to possess a powerful and reliable war deterrent," he told the Geneva forum.
"I am proudly saying that DPRK's nuclear force is capable of frustrating and countering any nuclear threats from the U.S. and it constitutes a powerful deterrent that prevents the U.S. from starting an adventurous war."
U.S. disarmament ambassador Robert Wood said: "The United States will not recognise North Korea as a nuclear weapon state.
"If the North wishes to return and be in the good graces of the international community, it knows what it has to do, it has to take steps toward denuclearisation of the Korean peninsula."
In an earlier speech on Tuesday, United Nations disarmament official Izumi Nakamitsu welcomed an easing of tensions between North and South Korea but called for further steps towards removing nuclear weapons from the divided peninsula.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.