North Korea announced yesterday that it was abandoning the armistice that ended the Korean War 56 years ago, and threatened war if there were any attempts to search its ships for weapons of mass destruction.

South Korea reported an increase in patrols by North Korean fighter jets on the border between the two states and there were reports of naval exercises close to the sites of previous skirmishes with the South Korean Navy.

The North’s pronouncements came after reports that it had restarted its plutonium reactor, which generates material for its nuclear arsenal, including the warhead that it tested on Monday. Pyongyang’s increase of tensions — a nuclear test, firing short-range missiles and now threatening war — is raising fears in the South of another direct military provocation.

“The Democratic People’s Republic of Korea has tremendous military muscle and its own method of strike is able to conquer any targets in its vicinity at one stroke or hit the US on the raw,” said a statement by the Korean People’s Army. “Those who provoke the DPRK once will not be able to escape its unimaginable and merciless punishment. In case the Armistice Agreement loses its binding force, the Korean Peninsula is bound to immediately return to a state of war from a legal point of view, and so our revolutionary armed forces will go over to corresponding military actions.”

Times Archive, 1950: Communists move into South Korea

The invasion by North Korea is being resisted by the South Korean forces, who have asked General MacArthur for assistance

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The warning came in response to South Korea’s announcement on Tuesday that it was to join the Proliferation Security Initiative, a multilateral effort to limit the spread of weapons of mass destruction by intercepting shipping and aviation. The North has threatened to abandon the armistice before, and over six decades South Koreans have grown used to the North’s aggressive rhetoric. But the latest moves may be the prelude to a further grand gesture by the North.

Government officials and security analysts anticipate the test launch of an intercontinental ballistic missile, a further nuclear test or a land or sea skirmish with South Korea along the border.

In response, the White House warned that North Korea risked further international isolation, while Hillary Clinton, Secretary of State, reiterated the US’s commitment to defending its allies. The US has 18,000 troops in South Korea. At the UN, ambassadors from the five permanent Security Council members — the US, Britain, Russia, China and France — as well as Japan and South Korea were working out the details of a resolution after the nuclear test this week.

The US has said that it wants “strong measures”, and though it was unclear last night how far China and Russia would co-operate, diplomats said that they were prepared to support new sanctions.

Although Sergei Lavrov, the Russian Foreign Minister, said that the world “must not rush to punish North Korea just for punishment’s sake”, Moscow did tell the North Korean ambassador that it had “serious concerns” about the nuclear test.

The South Korean Government said that the North’s fighter jets had more than doubled their sorties near the demilitarised zone, and the South Korean Yonhap news agency quoted sources as saying that North Korea was carrying out naval exercises close to the northern limit line, the disputed maritime border in the Yellow Sea.

Seoul’s Chosun Ilbo newspaper said that US spy satellites had detected steam at the Yongbyon nuclear plant since last month. This suggests that North Korea is reprocessing its spent plutonium fuel rods. If all 8,000 are processed, this could add one bomb to the 6 to 12 that North Korea is already estimated to have assembled.

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