BEIJING -- Millions of North Korean toddlers and unborn babies face permanent physical and mental damage if new aid is not pledged immediately to renew rapidly dwindling rations, the United Nations warned on Monday.

A slump in donations, worsened by a drop in Japanese aid, means that pregnant and nursing women and children under the age of two may soon see a complete halt in UN-donated grain, said Richard W.

Corsino, country director of the UN World Food Program (WFP).

"If we're not able to provide food to these groups then you'll see permanent damage," Corsino told a briefing in Beijing.

"This is both physical damage and impaired learning and this damage is irrecoverable. Once it occurs, it's finished," he said.

Overall more than four million North Koreans, including many elderly people, risk losing vital UN food donations as winter approaches, AFP quoted Corsino as saying.

Even if more food were to be pledged today, experience shows that at least two months would be needed before it translated into actual shipments of food, he said.

This means massive ration stoppages are already inevitable and will be felt by three million recipients over the next couple of months.

North Korea was the WFP's largest operation by far last year.

But even so -- and despite competing requirements from Afghanistan and Southern Africa -- more food aid is needed, according to the UN.

In September almost one million underfed primary school children are deprived of a daily 200-gram grain ration from the UN, while 140,000 elderly people have lost a 500-gram ration.

In October cereal distribution to nearly half a million kindergarten children and 250,000 pregnant and nursing women will end, and in November almost one million nursery children will see rations stop.

"We're basically running down the list of priorities. We're continuing to feed the most vulnerable of the vulnerable as long as we possibly can and these are the youngest children," Corsino said.

"But by November and December we're essentially going to be exhausted," he said.

Japan, formerly a major donor to North Korea, has not provided any aid so far this year.

Japanese Prime Minister Junichiro Koizumi said in March that Japan would not give food aid to North Korea unless progress was made over the alleged kidnapping of Japanese nationals by the communist state.

The WFP has so far this year seen contributions from 10 donor nations, including the United States, which has provided about 250,000 tons, and South Korea, with 100,000 tons.

China is also a major donor. It provides its aid outside UN channels, leaving aid officials with hazy estimates that Chinese assistance may be as high as 200,000 tons of cereal a year.

Stalinist North Korea has suffered serious famines since 1996, caused by a series of natural disasters that have compounded the near-total collapse of the country's planned economy.

According to some Western estimates, up to two million people have died from starvation and related diseases since then.

Government statistics indicate 45 percent of North Korean children under five are chronically malnourished, while a further four million school age children are also severely underfed.