North Korea is facing a "critical" food shortage, especially for children, the UN's food agency has said.
The World Food Programme's director for North Korea said the agency was unable to reach millions of North Koreans due to a shortfall in funding.
The director, Torben Due, said the WFP had received no new donations for North Korea since Pyongyang conducted a nuclear test in May.
He also said Pyongyang had barred the WFP from using Korean-speaking staff.
North Korea had given no reason for that decision, he added.
Mr Due told reporters in Beijing that the WFP had received only 15% of an international appeal for $504m (£306m) and had to cut back plans to provide food aid to 6.2 million North Koreans to 2.27 million.
North Korea has relied on food aid from China, South Korea and aid agencies to feed millions of its people since a famine in the 1990s resulted in the deaths of hundreds of thousands.
Recent flooding and the suspension of South Korean fertiliser aid shipments have hindered food production.
"We are now in the middle of the lean season in North Korea, where food supplies are low and it's a very difficult situation for many people in the country," Mr Due said.
Children were particularly at risk, he said.
"For children it is critical, and it means they do not have the nutrition required for growth," Mr Due said.
"We see an increase in the number of children being admitted to hospitals with severe malnutrition," he said.
He described a vicious circle in which malnourished children were growing up stunted with weakened immune systems and then giving birth to children with poor health.
The WFP's North Korea appeal had received no contributions since Pyongyang conducted a nuclear test on 25 May, he said.
"I understand to a certain extent why donors are questioning," he said.
"But my angle is as a humanitarian. Being a humanitarian organisation you should look at the needs of the people."
Mr Due said the WFP was now only allowed to operate in 57 counties within North Korea, instead of the previous 131.