South Korea's foreign minister called on the U.N. Security Council to expand sanctions on North Korea on Wednesday to punish what he called an escalating and increasingly threatening nuclear program.
Yun Byung-se called North Korea a "serial offender" and denounced Pyongyang's fourth nuclear test and latest long-range missile launch, carried out in January and February.
North Korea's Ambassador Se Pyong So said his country's nuclear program was designed to ensure peace on the divided Korean peninsula, and warned that more sanctions would bring a "tougher reaction".
Both men addressed the U.N.-backed Conference on Disarmament in Geneva hours before major powers were scheduled to vote at the U.N. Security Council across the Atlantic on a resolution to expand sanctions on North Korea.
The United States also condemned Pyongyang's actions.
"The international community stands united in its firm opposition to the DPRK's development and possession of nuclear weapons," Christopher Buck, deputy U.S. disarmament ambassador, told the Geneva talks.
"We do not and will not accept North Korea as a nuclear-armed state."
After nearly two months of bilateral negotiations, China last month agreed to support new measures in the Security Council to try and persuade its ally North Korea to abandon its atomic weapons program.
Pyongyang has been under U.N. sanctions since 2006 because of its nuclear tests and multiple rocket launches.
"It's no wonder that the Security Council will very soon put up a landmark resolution with the strongest ever non-military sanction measures in seven decades of U.N. history," South Korea's Yun said.
The credibility of the nuclear non-proliferation regime needed to be protected, he added.
"Even at this moment, Pyongyang is accelerating its nuclear weapons and missile capabilities from nuclear bombs and hydrogen bombs to ICBMs and SLBMs," he said referring to intercontinental ballistic missiles and submarine-launched ballistic missiles.
"We have heard Pyongyang officially state its intention not only to further develop its nuclear weapons and missiles but also to use them."
Japan's parliamentary vice-minister for foreign affairs, Masakazu Hamachi, said North Korea's actions had undermined the security of Northeast Asia and the rest of the world.
North Korea's envoy retorted that the nuclear program was "not directed to harm the fellow countryman but to protect peace on the Korean Peninsula and security in the region from the U.S. vicious nuclear war scenario."
"The more sanctions will bring about tougher reaction," So said.