Ri Yong Ho told the world body's annual General Assembly that North Korea had taken "significant goodwill measures" in the past year, such as stopping nuclear and missiles tests, dismantling the nuclear test site, and pledging not to proliferate nuclear weapons and nuclear technology.

"However, we do not see any corresponding response from the U.S.," he said.

"Without any trust in the U.S. there will be no confidence in our national security and under such circumstances there is no way we will unilaterally disarm ourselves first."

While Ri reprised familiar North Korean complaints about Washington's resistance to a "phased" approach to denuclearization under which North Korea would be rewarded as it took gradual steps, his statement appeared significant in that it did not reject unilateral denuclearization out of hand as Pyongyang has done in the past.