Rice and maize are the North's main staples, but rice output was expected to be below average because of erratic rains and low irrigation supplies, the FAO said in its quarterly Crop Prospects and Food Situation report.
Unfavourable weather conditions also diminished maize yields, it added.
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As a result the country would need to import 641,000 tonnes of food in the coming year, up from 456,000 tonnes this year, when it bought 390,000 tonnes and received 66,000 tonnes in food aid.
There was a widespread lack of access to food in the North, it said in the document.
"Food insecurity continues to remain a key concern, with conditions aggravated by the below-average 2018 main season output," it said.
Agricultural production is chronically poor in the North, which only has a limited supply of arable land.
The country has periodically been hit by famine, and hundreds of thousands of people died - estimates range into the millions - in the mid-1990s.
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North Korea was one of 40 countries - 31 of them in Africa - listed as in need of external assistance for food in the report.
UN agencies estimate that 10.3 million people in the North need humanitarian assistance. But donor funding has dried up in the face of political tensions over its weapons programmes, with critics saying that the provision of aid encourages Pyongyang to prioritise its military ambitions over adequately providing for its people.
David Beasley, the head of the UN's World Food Programme, said in May that there was undoubtedly a hunger problem in North Korea but it was not on the scale of the 1990s famine.
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