SAITAMA — A three-day U.N. conference on nuclear disarmament kicked off Wednesday in Saitama, a day after North Korea announced it had stopped disabling its atomic facilities.

"Reports of the development in North Korea, in addition to the nuclear issue in Iran, are major challenges to nonproliferation and nuclear disarmament efforts," Parliamentary Vice Minister of Foreign Affairs Masahiko Shibayama told the conference.

Blaming the halt on the U.S. unwillingness to lift sanctions against Pyongyang, North Korea suspended its denuclearization process and threatened to restore a reactor in Yongbyon, according to North Korea's state-run news agency KCNA on Tuesday.

"It is vital that the international community strengthen nonproliferation efforts with a stronger nuclear nonproliferation treaty to appropriately handle the issue," Shibayama said.

Organized by the U.N. Office of Disarmament Affairs and the U.N. Regional Center for Peace and Disarmament in Asia and the Pacific, the annual conference, held in Japan since 1989, gathers government officials from 17 countries and delegates from international organizations.

opening statement, Hannelore Hoppe, director and deputy to the high representative for the U.N. disarmament office, called for unity in the face of nuclear proliferation. The challenge is to "ensure nuclear energy is widely available for peaceful purposes" while eliminating any possibility of proliferation, she said.