The U.N.'s high representative for disarmament affairs is praising North Korea's decision to suspend its nuclear and ballistic missile tests and dismantle its nuclear sites as "welcome developments."

Undersecretary-General Izumi Nakamitsu said she hoped the moves would "contribute to building trust" and support dialogue.

Overall, however, she warned that "the threat of the use, intentional or otherwise, of nuclear weapons is growing."

She decried a "hiatus" in negotiations on arms control and disarmament, and expressed concerns that unless the trend is reversed, the world could return to a situation in which there are "no verified constraints on nuclear arsenals."

Nakamitsu spoke Monday at the kick-off of a two-week preparatory conference for the 50-year anniversary of the nuclear nonproliferation treaty, which has aimed to limit the spread of nuclear weapons, in 2020.