North Korea has assumed the rotating presidency of the world's top disarmament body for four weeks.
The move provoked criticism from conservative groups who say the country's nuclear weapons ambitions undermine its credibility for the role.
Geneva-based group U.N. Watch said North Korea chairing the 65-nation Conference on Disarmament was "asking the fox to guard the chickens."
But an official at the U.S. mission to the United Nations in Geneva, where the Conference on Disarmament is based, said the move was dictated by the rules of the 32-year-old body.
Spokesman David Kennedy said as far as the United States was concerned "it's business as usual."
The Conference on Disarmament has been stalemated since it wrote the nuclear test ban treaty in 1996.