North Korea intensified threats of an imminent conflict against the US and the South yesterday, warning foreigners to evacuate South Korea to avoid being dragged into “thermonuclear war”.

Once war breaks out, it will be an all-out war

The North’s latest message belied an atmosphere free of anxiety in the South Korean capital, where the city centre was bustling with traffic and offices were operating normally.

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, which threatens the US and its “puppet”, South Korea, on a daily basis, 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 agency quoted the Korea Asia-Pacific Peace Committee as saying. “The committee informs all foreign institutions and enterprises and foreigners, including tourists... that they are requested to take measures for shelter and evacuation in advance for their safety.”

None of the embassies in Seoul appeared to have issued any directives to their nationals and airlines reported no changes in their schedules.

Schools catering to foreign pupils worked without interruption.

The warning, read out on North Korea’s state television in a bulletin that interrupted normal programming, was the latest threat in weeks of high tension following UN sanctions slapped on Pyongyang 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 cooperation between the neighbours.

North Korean workers failed to turn up at the park yesterday. North Korea had said South Korea was trying to turn the Kaesong complex into a “hotbed of war”. Speculation remained high that the North may launch some provocative action this week – perhaps a missile launch or a nuclear arms test.