North Korea has rejected American food aid, the United States and a leading aid group said Tuesday, another sign of mounting tension as Pyongyang plans a rocket launch that Washington sees as cover for a long-range missile test. State Department spokesman Robert Wood said the North gave no reason for refusing to accept US food shipments. North Korea faces chronic food shortages and has relied on outside aid to help feed its 23 million people since famine reportedly killed as many as 2 million in the 1990s, a result of natural disasters and mismanagement. The five aid groups working in the North to distribute US food have been asked to leave the country by the end of the month, said Joy Portella, spokeswoman for the international aid agency Mercy Corps. Their distribution program had been scheduled to run until June. The announcements come during a North Korean nuclear standoff with the international community, and as the United States and others warn that any rocket test would trigger international sanctions. The North Korean launch is seen as a bid for President Barack Obama's attention as six-nation nuclear disarmament talks remain stalled.