By Stephanie Nebehay and Tom Miles
GENEVA (Reuters) - South Korea's foreign minister called on the U.N. Security Council to expand sanctions on North Korea on Wednesday to punish his neighbor for 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 dismissed the speech, saying his country's nuclear program was designed to ensure peace on the Korean peninsula and warned that more sanctions would bring a "tougher reaction".
Both men addressed 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.
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 told the Geneva forum.
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 envoy at the conference, 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.
(Reporting by Tom Miles and Stephanie Nebehay; writing by Stephanie Nebehay; Editing by Jeremy Gaunt and Andrew Heavens)