The UN is cutting in half its daily rations in Sudan's Darfur region because of a severe funding shortfall.
Malnutrition is on the rise again in Darfur
From May the ration will be half the minimum amount required each day. The cut comes as the UN said Darfur's malnutrition rates are rising again.
Nearly 3m people depend on food aid after being driven off their land.
But little has come from the EU and nothing at all from any of Sudan's partners in the Arab League, except Libya, the World Food Programme says.
"This is one of the hardest decisions I have ever made," James Morris, head of the WFP, said.
Despite a ceasefire and on-going peace negotiations, large areas of Darfur are now affected by fighting between government forces, militias and rebels.
This is also hampering the delivery of food and other aid operations.
"Haven't the people of Darfur suffered enough? We are adding insult to injury," Mr Morris said as he explained that despite appeals to donors, the WFP has received only a third of the money it needs.
DARFUR DAILY FOOD RATIONS
Minimum requirement: 2,100 kilocalories per person
New amount: 1,050 kilocalories per person
Cut by half: Cereals, blended fortified food and oil
Cut by three-quarters: Pulses, sugar and salt
More than 6.1m people across Sudan require food aid - more than any other country in the world.
The bill to feed them all is $746m.
The United States has provided $188m, but little has been received from elsewhere.
The EU says it has allocated 48m euros ($60m) for the whole of Sudan this year, while the UK will donate £49m ($88m) through various aid agencies.
The ration cut is designed to ensure that some food lasts through the "hunger season" between July and September.
"We have been pushed into this last resort of ration cuts in Sudan so we can provide the needy with at least some food during the lean season," Mr Morris said.
The BBC's Jonah Fisher in the capital, Khartoum, says even if more money was to be immediately promised, Darfur's location, in the centre of Africa, means it could still take up to four months for the rations to arrive.
Earlier this week, Ted Chaiban, head of Unicef's mission to Sudan, said in the last three months alone, there had been 200,000 people newly displaced in Darfur.
Aid agencies last year managed to bring the malnutrition rate below the emergency threshold of 15% but south Darfur was seeing those figures again, he said.
The African Union has set a 30 April deadline for the government and rebel groups to accept their draft peace agreement which addresses power-sharing, wealth-sharing and security.