The World Food Programme will have to stop delivering aid to starving North Koreans by July if it does not receive more donations immediately.

Although a senior United Nations official said the Pyongyang office was at risk of closure, Torben Due, the programme's North Korea representative, said he remained optimistic despite growing donor fatigue.

“The WFP can continue to support around 1.4m children and pregnant women with fortified foods until the end of June. However, new contributions are required now or the operation will come to a standstill in July. We are hopeful that donors will come forward with contributions, given the situation,” he told the Financial Times.

In 2008 the WFP hoped 6.2m people would receive such aid but found it ever harder to attract donations. Annual aid to North Korea is equivalent to $4.50 (€3.30, £3) per person across the population. The average across other low-income countries is $37 per person.

The WFP has survived such funding crunches in the past, but UN officials fear donors have now become exasperated with North Korea, which expelled US non-governmental organisations last March. Pyongyang has severely restricted aid workers' access, has demanded they give longer notice before making rural visits and has barred teams from using their own Korean speakers.

Rocky relations with the US and South Korea after Pyongyang launched a long-range missile last April and tested an atomic warhead in May have further discouraged donations.

The US, once the leading food donor, has said it will not supply cereals until North Korea resumes proper monitoring, allowing aid agencies to track the final recipients.

North Korea's harvests cannot feed all its people and in recent years the annual food deficit was about 1m tonnes. People are chronically malnourished and as many as 1m are believed to have died during famine in the 1990s.

It is hard to determine the scale of malnutrition but Kim Jong-il, the country's dictator, made a very rare apology this year for failing to deliver “rice and meat stew” to the people. Food markets were thrown into disarray late last year by a currency redenomination but Mr Due, based in Pyongyang, said these seemed to be returning to normal.

Hyun In-taek, South Korea's unification minister, said last week that China had recently supplied large food shipments to its neighbour, where it fears instability. There are strong indications Beijing is increasing its infrastructure and commercial investment in North Korea.