Millions of North Koreans are at risk of starvation, thanks to new restrictions on aid imposed by the country’s dictatorship and the drying up of international assistance after its provocative nuclear test.

The UN’s World Food Program (WFP) said that it has received barely $75 million dollars, (£45 million) 15 per cent of the $504 million it needs to feed 6.2 million North Koreans during the lean months up to the November harvest. This target in itself was already fewer than the 9 million people who are estimated to be in need.

For the time being there is no risk of a repeat of the famine of the late 1990s, in which hundreds of thousands, and by some estimates millions, died. But the food shortages threaten to cause long term problems among children, who are especially vulnerable to the physical and intellectual stunting which can be caused by malnutrition.

“We have not really received any contributions after the nuclear test was carried out,” said Torben Due, WFP’s country director for North Korea, at a press conference in Beijing. “It is a very serious problem for the population … as they do not have enough to eat.

“For adults, it doesn't mean a lot if you live for a few months on a diet of cereals and vegetables, but for children, it is critical. We see an increase in the number of children being admitted to hospitals with severe malnutrition.”

WFP’s work has been made all the harder by new restrictions imposed by the North Korean government. It is permitted to work only in 57 counties, compared to 131 formerly. And it has been banned from employing Korean speakers, apparently out of fear that they may suborn North Koreans into whom they come into contact. As a result, the organisation has 16 employees in the country, down from 59.

North Korea’s nuclear test on May 25 was followed by a series of provocations, including the testing of short range missiles and a threat to abandon the armistice which brought to an end the 1950-53 Korean War. It was met with international outrage, especially in the US, Japan and South Korea, and the promise of stiff new sanctions against North Korea and those who support it.

The US Treasury announced that it was blacklisting a North Korea and Iranian company which it claimed, were front for laundering funds related to weapon proliferation. The two firms – Namchongang Trading Corporation and Iran's Hong Kong Electronics – will have any US assets seized and US companies will be forbidden by law from doing business with them.

“Today's action is a part of our overall effort to prevent North Korea from misusing the international financial system to advance its nuclear and missile programs and to sell dangerous technology around the world,” said Stuart Levey, Treasury undersecretary for terrorism and financial intelligence.

Meanwhile a North Korean ship which the US said it suspected of carrying sanctioned military goods towards Burma reversed course on Sunday, according to news agency reports. The Kang Nam 1 was the first ship to be monitored under the recent sanctions. “Our ships are sacred and impregnable places where our sovereignty reigns,” North Korea’s Rodong Sinmun (Workers’ Newspaper) wrote. “If anyone hurts them, it would be considered a grave military provocation against us. This kind of action will immediately meet with our self-defensive military actions.”

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