War might be on the mind of President Kim Jong-un of North Korea, but diplomats in the capital Pyongyang are keeping a stiff upper lip despite all of his bellicose behaviour.

Yesterday there was no sign that any of the embassies or legations were closing shop, despite warnings from officials that their safety could not be guaranteed after Wednesday. At the end of a week that had seen Kim giving dire warnings about attacking his enemies, notably South Korea and the US, it was a case of business as usual.

"We don't believe there's any foreign mission about to leave Pyongyang," said a diplomatic source. "Most foreign governments view the North Korean message as a way of ratcheting up tension on the Korean peninsula."

And yet, despite the calm that was matched in the South Korean capital Seoul, the latest outburst of warmongering has gone beyond the usual rhetoric employed by the North Korean leadership. This time it has been backed by the redeployment of two medium-range missiles to the east coast and by the partial mobilisation of the country's million-strong army.

While these forces would be no match for the US, which has deployed nuclear-capable B2 and B52 bombers to the region, any build-up in this volatile part of the world is always dangerous – not least because the two Koreas are still officially at war 60 years after the last conflict came to an end. In a television address to the country on Friday, Kim told fellow North Koreans that the country needed to "absolutely guarantee the quality of our artillery and shells to ensure a rapid pre-emptive attack on our enemies".

At the same time, government officials used the North Korean government daily newspaper Minju Joson to warn the tension was the fault of the US because it had embarked on training exercises with South Korean forces. "This is aimed at igniting a nuclear war against it through a pre-emptive strike," said the editorial. "The prevailing situation proves that a new war, a nuclear war, is imminent on the peninsula."

Another reason for Kim's anger was the decision taken by the UN last month to impose additional sanctions on North Korea. This is a more credible reason for the current outburst than the war gaming, which is a regular occurrence. Since coming to power last year, Kim has made no secret of his nuclear ambitions and his willingness to ignore international disapproval. Although the UN regularly raps his knuckles by imposing economic sanctions of increasing severity, these have made little impact on his regime. Not only do they leave the upper echelons unaffected, but the worst of the sanctions are cancelled by China's continuing support.

Although the Beijing regime is becoming increasingly irked by Kim's unruly behaviour, it has no interest in having him unseated. For a start, he is a useful bulwark against Washington's growing interests in the region – President Barack Obama began his second term by announcing that the Pacific would be a new focus of US diplomacy. Any change in the status quo could also lead to thousands of North Koreans fleeing over the long and porous border into China, precipitating a crisis the Chinese authorities would be unable to control. It is also true that Russia would not welcome regime change as North Korea could then fall into Washington's sphere of interest through Seoul.

So far, though, the Chinese have shown little interest in curbing Kim and seem content to let the current crisis run its course. That, too, seems to be the line taken by the US State Department, where officials are relaxed about the possibility of further escalation. At the very least they are anticipating the test-firing of another missile, perhaps one of the two that have been redeployed to the east coast. While this would do little if any damage – provided it fell in the sea – it might satisfy Kim's military pride by demonstrating to his people that he has no fear of the US or South Korea.

Any other response seems unlikely because a military move would be suicidal. North Korea probably does possess a rudimentary nuclear device but the delivery systems are incapable of delivering it to a specified target. That leaves his conventional forces, which are based on an army one million strong with a further five million reservists to back it up. He also possesses substantial artillery and armoured forces, which are capable of doing considerable damage and would take some stopping.

Even so, US forces showed in Iraq 10 years ago they are well capable of destroying opposition armed with Cold War-style conventional weapons. And as a US diplomatic source explains: "Kim is not stupid. He may want to take a swing at Uncle Sam but he saw what happened to Saddam [Hussein] and he won't want to take that route."