ABC News' Kirit Radia Reports: North Korea has informed the United States it no longer wishes to receive American food assistance, the State Department said today. "North Korea has informed the United States that it does not wish to receive additional U.S. food assistance at this time," acting spokesman Robert Wood told reporters, adding that the notification came in "the last couple of days." Wood said no further reason was given for the decision. American non-governmental organizations that have worked in North Korea to distribute food assistance have also been informed they will be asked to leave the country, US officials said. The groups were scheduled to leave at the end of May, but have been told they must depart sooner than that, officials said. "We will work with U.S. NGOs and the North Korean counterparts to ensure that food that's already been delivered -- or food that's already in North Korea is distributed to the intended recipients," Wood said. The US re-started food aid to North Korea last May after a two-year halt, in part due to concerns over inadequate monitoring to ensure that food aid reaches those in need. Since then 169,000 metric tons of US food assistance have been sent to North Korea. The latest shipment of about 5,000 metric tons of cooking oil arrived just this past January. The State Department today expressed frustration at the North Korean move. "Clearly this is food assistance that the North Korean people need. That's why we're concerned. You know, this humanitarian assistance that we provide to the North has nothing to do with the six-party talks. This is about our true humanitarian concern for these people," Wood said. One official said the US was in talks with the North Koreans to try and convince to reverse the decision.