BEIJING, China (CNN) -- The first survey on food and nutrition in North Korea since the country granted broad access to aid groups shows millions of people are going hungry, with households reducing their food intake and more children becoming malnourished.

The survey -- conducted jointly by the United Nations' World Food Program and the Food and Agriculture Organization -- also shows a widening gap between how much food North Korea is able to produce or purchase and how much its population needs.

The WFP called it the largest food gap since 2001 for the country of 23 million.

"Millions of vulnerable North Koreans are at risk of slipping towards precarious hunger levels," said Jean-Pierre de Margerie, the WFP's country director for North Korea, at a news conference in Beijing.

"The last time hunger was so deep and so widespread in parts of the country was in the late 1990s."

The three-week survey covered 53 counties in eight of North Korea's nine provinces, the WFP said.

Experts visited hundreds of households, child institutions, and hospitals across the country in what the WFP called the most comprehensive assessment of food and nutrition in the country since 2004.

The U.N. agencies were allowed to conduct the survey under a deal signed in May by the United States, the United Nations and North Korea to give outsiders much greater access to the country to deal with the its food crisis.

As part of the same deal, the United States in June sent a ship carrying 38,000 tons of food to North Korea. The delivery was part of 500,000 metric tons of food the United States promised for North Korea over a one-year period.

The WFP said flooding in August 2007 and successive poor harvests, compounded by soaring prices for food staples, are contributing to the rising hunger levels.

The organization said it is expanding food distributions to reach 6.4 million people, up from the current 1.2 million it has been serving.

The WFP said three-quarters of the families surveyed have reduced their food intake. Most have cut protein from their diets and are living on cereals and vegetables alone.

Even that diet has become difficult to manage as food prices soar, the WFP said. Rice now costs almost three times more than a year ago, and maize has quadrupled.

More people are now scavenging for wild foods, which provide little nourishment and are difficult to digest, de Margerie said. Diarrhea caused by wild food consumption is also one of the leading causes for malnutrition in children younger than 5, the WFP said.

That is one factor in the increase in the number of malnourished and ill children being admitted to hospitals and institutions, the agency said.

"Food assistance to reach the hungry is urgently needed," de Margerie said.

The WFP is urging countries to step up donations to North Korea to help the country get through the upcoming autumn harvest.

Under a letter of understanding, North Korea agreed to open much more of the country to aid and to allow random surveys to see whether the intended beneficiaries are actually getting the food. The number of foreign personnel working to provide food aid was also allowed to increase from 10 to 60.

North Korea previously allowed food aid to 50 counties in the country, with restrictions; under the new agreement, it will allow aid to 150 counties, covering most of the country.

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