North Korea has formally told the UN it no longer needs food aid, despite reports of malnutrition in the country.
It is unclear what impact the loss of food aid will have
Deputy Foreign Minister Choe Su-hon said the country now had enough food, due to a good harvest, and accused the US of using aid as a political weapon.
Top UN relief co-ordinator Jan Egeland said an "abrupt" end to food aid would harm North Korea's most vulnerable.
Pyongyang's move comes as the world community continues to urge it to give up its nuclear ambitions.
Analysts say North Korea might be worried that accepting more food aid now could be perceived as a sign of weakness.
The North may also have lost patience with efforts by foreign agencies to monitor deliveries of food, according to the BBC's Seoul correspondent, Charles Scanlon.
In recent years, the UN and other international agencies have been feeding up to six million of the poorest and most vulnerable North Koreans.
But these organisations have long struggled for access to one of the world's most closed societies.
Even at the height of a famine in the mid-1990s, which may have killed two million people, they were tightly restricted and refused entry to large parts of the country.
Now the authorities are cracking down altogether, our correspondent says.
After meeting UN Secretary General Kofi Annan in New York on Thursday, Choe Su-hon told reporters: "We requested him to end humanitarian assistance by the end of this year."
He said that the North wanted all foreign NGOs out by the end of the year, and added that the UN was to stop delivering food aid and to focus on long-term development instead.
Mr Egeland urged North Korea to reverse its decision, saying he was especially worried about the country's children.
"Our concern is they (North Koreans) will not be able to have enough food. We are very concerned because we think this is too soon and too abrupt," he said.
Gerald Bourke, a spokesman for the WFP, said that UN staff were currently discussing with the North Korean government what this meant in practice - adding that he was hopeful that current food-for-work and other community-based projects would class as longer-term development.
"We're also talking to donors to see how much they still want to help us in this way," he added.
Mr Bourke said that despite Mr Choe's assertion of a better harvest in North Korea this year - and his pledge that the government was "prepared to provide the food to all our people" - there was still a considerable need for food aid.
"North Korea has a substantial and chronic food deficit," Mr Bourke said, adding that malnutrition rates, especially for mothers and young children, were still very high.
Mr Choe also accused other countries, especially the US, of attempting to "politicize humanitarian assistance, linking it to the human rights issue".
He said this constituted interference in the internal affairs of the country.
Washington rejected the suggestion it was mixing politics with relief work.
The North insists it had a good harvest this year
"All US decisions are based on... the need of the country involved, competing needs elsewhere and our ability to ensure that the aid gets to people who need it most," a State Department statement said.
Another problem which analysts believe may have led to the North's decision to ask foreign organisations to leave is the extensive surveying these groups are required to do, to ensure their money is being well-spent.
"Part of the problem is with our monitoring people moving around the country," Mr Bourke conceded. "This is and has been a concern for them."
In contrast, China and South Korea provide huge food shipments to North Korea without overseeing where it ends up.
The South says it gives such aid as part of a strategy to promote political reconciliation.
But diplomats and aid workers say these generous shipments have undermined the multilateral effect.
According to our correspondent, there is concern that if monitoring stops, so too will surveys to check the food gets to those most in need.