Foreign Minister Yun Byung-se warned North Korea of grave consequences following its threat of a new nuclear test. He urged the Kim Jong-un regime to take a “path to cooperation” or face deeper international isolation.

North Korea said on Sunday it will not rule out a “new type of nuclear test” to further strengthen its nuclear deterrence in protest of the U.N. Security Council’s denunciation of its ballistic missile tests last week.

Officials and analysts said there are no “imminent signs” of the North’s nuclear test yet.

An analysis of satellite imagery last week by 38 North, a website run by the U.S.-Korea Institute at Johns Hopkins University, said that recent excavation activities at an atomic test site in the northeast town of Punggye may indicate that Pyongyang is building a tunnel complex to conduct multiple tests or explosions on a “much more regular basis.”

“North Korea’s nuclear program remains the biggest threat at this very moment,” Yun told a meeting of heads of overseas missions.

“It’s up to the North Korean leadership whether to carry out a nuclear test, but that choice will significantly determine the country’s future.”

An official at the U.S. Department of State also warned against any move that breaches U.N. Security Council resolutions, calling on the North to comply with its international obligations and refrain from threatening regional peace and security, according to Yonhap News.

On Sunday, Seoul issued a statement expressing “grave concerns” over the North’s threat of another detonation and condemning its recent firing of short- and medium-range missiles.

“North Korea should bear in mind that it will face consequences if it presses ahead with the nuclear test in disregard of stern demands from its neighbors and the international community,” the Foreign Ministry warned.

In a statement Sunday carried by the North’s official Korean Central News Agency, the North’s Foreign Ministry said, “(We) will not rule out carrying out a new type of nuclear test to further bolster nuclear deterrence,”

Last Thursday, the UNSC issued its verbal condemnation, saying Pyongyang violated its resolutions banning any launches using ballistic missile technology. It also said it would continue to consult on an “appropriate response.”

Earlier this month, the North threatened to “show off” its nuclear deterrence capability. But it is the first time for it to mention the possibility of a fourth nuclear test, which would further sophisticate its ability to build nuclear warheads.

By Shin Hyon-hee  (heeshin@heraldcorp.com)