North Korea has been placed under martial law and Kim Jong-un has told his front-line troops to "be ready for a war," according to South Korean media reports.

Kim Jong-un AP In an emergency meeting of his top defence and security officials on Saturday, the North Korean leader issued a series of orders that included the conclusion of preparations for a new nuclear test, the Joongang Daily reported.

North Korean state media has also reported that Kim ordered his officials to take "effective, high-profile state measures."

While it has been anticipated that Pyongyang will go ahead with what will be the regime's third nuclear test, in spite of international pressure to refrain from doing so, analysts had predicted that the blast would be timed to coincide with the birthday on February 16 of Kim Jong-il, the former leader who died in late 2011, or the inauguration of the new government in South Korea nine days later.

The reports now suggest that the demonstration of North Korea's nuclear prowess is more imminent.

In March 1993, North Korea placed the nation under martial law shortly before it announced it was withdrawing from the Treaty in the Non-Proliferation of Nuclear Weapons. The regime also ordered its troops to be ready for war.

Pyongyang's preparations have been corroborated by South Korean government officials and sources in Beijing, with surveillance images suggesting that the mouth of the shaft has been sealed in readiness for the test at the Pyunggye-ri site.

North Korea conducted its first nuclear test in October 2006 and carried out a second underground detonation in May 2009.

This latest test is in direct response to international criticism of its launch of a rocket in December that Pyongyang claimed was for peaceful purposes. The United Nations Security Council concluded unanimously that it was a test-firing of an intercontinental ballistic missile.

Lee Myung-bak, the president of South Korea, ordered the military to be ready to make a "strong response" to any provocation from North Korea.

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