An escalating war of words across the world’s last Cold War, nuclear-armed border spiraled dramatically yesterday when North Korea threatened to wreak total destruction on its neighbour to the south.

“Our military will not sit idle until warmongers launch a pre-emptive strike,” the official news agency in Pyongyang reported a senior military commander as saing, “everything will be in ashes, not just a sea of fire, if our advanced pre-emptive strike once begins.”

The threat was among the most direct and bellicose statements from Pyongyang since North Korea test-fired an atomic device in late 2006. International efforts since then to persuade the country’s enigmatic dictator, Kim Jong il, to abandon his weapons programme have repeatedly stalled.

The threat also marked a fourth day of rapidly deteriorating relations on the Korean peninsula, which remains technically still at war despite more than 50 years of often uncomfortable armistice.

The two countries – the prosperous, modern South and the unpredictable Stalinist Democratic People’s Republic of Korea (DPRK) – continue to glare at one another across the world’s most heavily armed border.

A note sent by a North Korean military delegation to its South Korean counterpart on Saturday, said that “these outbursts are the gravest challenge ever in the history of the inter-Korean relations and a reckless provocation little short of a war declaration against the DPRK.”

Sunday’s warning followed remarks in Seoul earlier in the weekend in which the head of South Korea’s military vowed to conduct a pre-emptive strike on the suspected North Korean nuclear weapons site if Pyongyang tried to attack with atomic weapons.

The office of the chairman of the South’s joint chiefs of staff later explained that it was a statement of general principles, rather than a hint that the South was planning any unprovoked attack on the North. Pyongyang said that it would suspend all cross-border dialogue unless the remarks were withdrawn and an apology issued.

Although the communist regime of Kim Jong Il has regularly used this form of extreme language in the past, long-term North Korea experts said that its renewed appearance of the past few days should be treated with some caution.

The row, which has already seen 11 South Korean officials expelled from a joint economic “friendship” zone by the North, is thought to be a test by Pyongyang of the mettle of the new president in Seoul.

On Friday the DPRK test-fired a salvo of short-range missiles, reprising an act that has traditionally provoked outrage in Seoul and placed South Korean leaderships under immense domestic strain.

Lee Myung Bak was elected to the South Korean presidency in December last year on promises of a stronger economy. But he made little secret that his view towards North Korea and Kim Jong il would be far less conciliatory than his predecessor’s.

His response to the current escalation of tensions will be closely scrutinised on both sides of the demilitarized zone that splits the peninsula.

In addition to the deeper conflict over Pyongyang’s atomic weapons programme, the most recent row has ignited an argument over a line in the Yellow Sea that has never been recognised by North Korea: officials in Pyongyang said on Friday that “armed conflict may break out at any moment” over the boundary.

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