Han Tae Song told the conference in Geneva on Tuesday that the Punggye-ri nuclear test site in North Korea will be dismantled within 10 days.
Some observers believe that Han's remark suggests that the North offered to be part of the Comprehensive Nuclear Test Ban Treaty (CTBT) ahead of its summit with the USA slated for next month.
North Korea is one of the so-called Annex 2 states that must ratify that treaty for it to come into force.
According to researchers, the demolition began with the least-significant objects, and the more important buildings and structures remain in place. North Korean authorities have promised to demolish its nuclear test site in the period from 23 to 25 may, depending on weather conditions.
"The discontinuance of the nuclear test is an important process for the worldwide disarmament, and the DPRK will join the global desire and efforts for the total halt to the nuclear test", the North's Korean Central News Agency wrote last month.
During his speech at the disarmament conference, the North Korean ambassador to the United Nations also said North Korea was hoping to further diffuse military tensions on Korean Peninsula.
He said the North will join the world in its wish and efforts to ban all nuclear explosions for both civilian and military testing.