NORTH KOREA has intensified threats of an imminent conflict against the US and the South, warning foreigners to flee South Korea to avoid being dragged into "thermonuclear war".

However, Pyongyang has shown no sign of preparing its 1.2 million-strong army for war, indicating the threat could be aimed partly at bolstering Kim Jong-un, 30, the third in his family to lead the country.

The North is marking anniversaries this week that could be accompanied by strong statements or military displays.

The warning to foreigners in the South, reported by the KCNA news agency, said once war broke out "it will be an all-out war, a merciless, sacred, retaliatory war to be waged by (North Korea).

"It does not want to see foreigners in South Korea fall victim to the war," the country's Korea Asia-Pacific Peace Com-mittee was quoted as saying.

None of the embassies in Seoul appeared to have issued any directives to nationals and airlines reported no changes in their schedules. Schools catering for foreign pupils worked without interruption.

The warning, read on North Korea's state television, was the latest threat in weeks of tension after UN sanctions for its latest nuclear arms test.

It followed the North's suspension of activity at the Kaesong joint industrial park just inside North Korea, all but closing down the last remnant of co-operation between the neighbours. North Korean workers failed to turn up yesterday.

In a previous appeal, its authorities urged diplomats in Pyongyang to leave on grounds their safety could not be assured beyond today. None appeared to have taken any such action.

A spokeswoman for South Korea's presidential Blue House dismissed the warnings, saying no-one felt under threat.

A Seoul government source said a North Korean medium-range missile, reported to have been moved to the east coast, had been tracked and was believed to be ready for launch.

But a US embassy official in Seoul said a directive issued last week saying there was no imminent threat to Americans in South Korea remained valid.

World leaders have expressed alarm at the crisis and the prospect of a conflict involving a country claiming to be developing nuclear weapons.

China, the North's sole diplomatic and financial ally, issued a new call for calm and restraint, although Beijing's leaders have shown increasing impatience with Pyongyang.

A Russian foreign ministry spokesman said Moscow was in solidarity with all G8 industrialised countries "as regards the rejection of Pyongyang's current provocative and bellicose line of conduct".

UN Secretary General Ban Ki-moon described the situation as very dangerous. He said: "A small incident caused by mis-calculation or misjudgment may create an uncontrollable situation".

The North is also angry at weeks of joint US-South Korean military exercises off the coast of the peninsula.

Employers at Kaesong faced uncertainty as the 53,000-strong North Korean workforce stayed away.

A spokesman for textile company Taekwang Industrial and at least two other firms said production had stopped.

The complex generates $2 billion (£1.3bn) in trade for the impoverished North.