SEOUL, South Korea — About 40 percent of North Korea’s population is in urgent need of food aid after the country suffered its worst harvest in a decade, the United Nations said on Friday, even as its regime defied international sanctions in order to keep its nuclear weapons program.

The bad harvest left North Korea with a 1.36 million ton shortage of grain, forcing its government to reduce daily state rations to less than 11 ounces per person in January, compared with 380 grams a year earlier, the World Food Program and the Food and Agriculture Organization said in their joint assessment. Rations may decline further between July and September, when they are typically lower, the agencies said.

“The situation could further deteriorate during the lean season from May to September, if no proper and urgent humanitarian actions are taken,” the United Nations relief agencies said.

North Korea’s state ration system collapsed during the famine of the late 1990s, which killed up to three million people by some estimates. Millions of North Koreans have since learned to fend for themselves, securing food through unofficial markets. But millions still depend on the ration system, including soldiers and workers in state-run factories.