North Korea on Sunday conducted its sixth nuclear test, claiming that it was now capable of producing intercontinental ballistic missiles fitted with thermonuclear warheads.

Pyongyang’s latest provocation came in the face of international condemnation and sanctions, applied even by its traditional ally China. 

South Korea’s President Moon Jae-in convened the National Security Council meeting at 1:30 p.m.

Moon’s top national security adviser Chung Eui-yong also held a telephone conversation with his US counterpart Herbert McMaster, Cheong Wa Dae said.

According to Chung, Moon called for government officials to draw up stronger measures to punish North Korea for continued provocations. 

"In collaboration with the international community, draw up punitive measures of the highest order," Moon was quoted as saying by Chung. 

Chung also said that Moon ordered the attending officials to use all diplomatic measures possible to "isolate North Korea completely" to bring about "irreversible" end to Pyongyang's nuclear program.

In a “critical announcement” held at 3:30 p.m., North Korea’s state media claimed that the test was a “complete success of a hydrogen warhead for an ICBM.”

Sunday’s nuclear test took place hours after North Korea claimed that it had completed its thermonuclear technologies, and was now capable of producing “powerful nuclear weapons at will.”

The latest test comes almost exactly a year after North Korea’s fifth nuclear test, which it also claimed was a hydrogen bomb. The fifth nuclear test, conducted on Sept. 9, 2016, had created seismic waves measuring magnitude 5.3.

North Korea’s nuclear test was detected by South Korean, Chinese and other authorities, at about 12:29 p.m.

According to Seoul’s Joint Chiefs of Staff office, seismic waves measuring magnitude 5.7 were detected from Punggye-ri, North Hamgyong Province in northeastern region of North Korea at 12:29 p.m. Punggye-ri is the site of Pyongyang’s previous nuclear tests.

Those readings would put the size of the explosion at several times larger than previous North Korean tests. It could be much larger still if the reading of 6.3 magnitude by the United States Geological Survey is correct. The Chinese government also put the size of the tremor at magnitude 6.3.

According to Seoul’s Meteorological Administration, the seismic activity detected in Punggyeri had the characteristics of an induced earthquake. The military announced that it suspected North Korea has conducted a nuclear test and that military readiness in South Korea had been raised.

“The military has raised surveillance and readiness against North Korea, and is reviewing executing various response measures in cooperation with the US,” the South Korean JCS said in a statement.

Moon, who had called for dialogue with North Korea during his election campaign, has been pushed to take an increasingly harder stance following series of provocations.

Following North Korea’s missile launch in July, Moon ordered for more THAAD launchers to be deployed in Seongju, North Gyeongsang Province. After a North Korean missile flew over Japan’s airspace to land in the Pacific on Aug. 29, Moon ordered the military to conduct a show-of-force exercise.

While Moon’s approach to North Korea hardens, talk of bringing US’ tactical nuclear weapons back into South Korea has reemerged, which has long been championed by the conservatives. However, but North Korea’s increasingly serious provocations have prompted the current liberal administration’s Minister of National Defense Song Young-moo to discuss the issue with his US counterpart.

Japan responded immediately to the suspected nuclear test with Prime Minister Shinzo Abe calling a national security meeting.

“There is possibility that North Korea carried out a nuclear test today. If the nuclear test is proven true, it cannot be countenanced,” Abe told reporters shortly after he was briefed on the issue, saying that Japan protested strongly against Pyongyang’s actions.

At the national security meeting, Abe reportedly told government agencies to collect and analyze intelligence, and to cooperate closely with concerned nations including South Korea, China, Russia and the US.

By Choi He-suk (cheesuk@heraldcorp.com)