North Korea's third nuclear test and threats of military action are "completely unacceptable", U.N. Secretary-General Ban Ki-moon said in remarks published on Saturday, urging Pyongyang to feed its people and seek peace with South Korea.
North Korea threatened the United States on Thursday with a pre-emptive nuclear strike and has scrapped the armistice with Washington that ended hostilities in the 1950-53 Korean War.
That followed its third nuclear test on February 12, in defiance of U.N. resolutions, drawing further U.N. Security Council sanctions against the reclusive East Asian state.
Asked by Austria's Profil magazine about North Korea's nuclear test, military exercises and threats, Ban, a former South Korean foreign minister, said: "I find this completely unacceptable and it is also a challenge for the international community."
He said in an interview with Profil that he had urged the North Korean leadership to focus on the welfare of its own people in the face of serious economic problems.
"There is a serious humanitarian crisis in North Korea. Many people suffer from malnutrition," he said, calling for dialogue and peaceful exchanges with South Korea.
"(South) Korea has just elected a new president. That would be good timing for the leadership of the two parties to the conflict to discuss seriously how to encourage national reconciliation and to reduce tensions on the Korean peninsula, also in view of a possible reunification of the country."
North Korea formally rejected a U.N. Security Council resolution on Saturday demanding an end to its nuclear arms program and China called for calm, saying sanctions were not the "fundamental" way to resolve tensions.
Pyongyang said it would pursue its goal of becoming a full-fledged nuclear weapons state, despite the sanctions which were unanimously imposed on Friday by the Security Council.
Turning to a separate dispute, Ban said he had urged Iran to address international concerns that its nuclear program could have a military dimension, something Tehran denies.
Ban said he found it positive that talks between Iran and world powers in Kazakhstan last week had produced an agreement to meet again, first at an expert level.
"But I have made it clear to the leadership in Iran that the Iranian government must do everything possible to convince the international community and to establish confidence about the nuclear program," he said.
"There are still concerns about whether the nuclear program is really only for peaceful purposes. I told Foreign Minister (Ali Akbar) Salehi that it is the responsibility of Iran to restore trust about it."
The two met in Vienna last week at a U.N. conference.