North Korea has cut food rations to just half the amount recommended by the World Food Programme, the UN food agency says.
Private markets have sent food prices rocketing
WFP monitors say government handouts have been cut from 300g (10.5oz) of cereals a day to 250g.
The UN says 16 million North Koreans rely on the rations.
A WFP spokesman told BBC News that many people would be unable to supplement their allocation of maize, rice and potatoes with any meat or vegetables.
"Prices of basic foods in private markets have increased substantially - they're beyond the means of many people. Supplementing the ration has been increasingly difficult," said Gerald Bourke, the WFP's public affairs officer for Asia.
Most of the worst-affected people are in North Korea's cities, he told the BBC News website.
A UN report last year said private farmers' markets, which were meant to alleviate chronic hunger, had instead sparked spiralling inflation.
It said 1kg (2.2lb) of rice now costs 30% of the average monthly wage.
HOW MUCH IS 250 GRAMS?
Two medium-sized bowls of rice; total 350 calories OR
Five small potatoes or two medium-sized potatoes; total 180 calories
The reasoning behind Pyongyang's decision to cut rations is unclear.
But North Korea watchers speculate that the government may be acting to encourage the focus of food distribution towards the farmers' markets - despite the fact that in the short term this may leave some people hungry.
They say farmers have been holding back some of their harvest to sell on the farmers' markets, where they can receive much better prices than by selling to the government-run distribution system.
It has been suggested that the government's action may be part of recent initiatives to allow market forces to begin asserting themselves in the hitherto strictly state-controlled country.
The cuts come despite what was thought to be the impoverished country's best harvest in 10 years in September and October.
Mr Bourke said the ration level is set every month, but early indications suggested that the cuts would last until the middle of 2005.
"As of now we have sufficient cereals to feed all the six-and-a-half million people we seek to feed in North Korea until June.
"But those rations are projected on a basis of public distribution of 300g - so we need to see how this changes now," he said.