Five private relief groups are protesting the U.S. government's failure to send food aid to North Korea, saying they don't understand why the aid is being withheld.

The five American NGOs said in a statement Tuesday the Obama administration has failed to act in spite of repeated warnings that a potentially catastrophic food crisis in emerging in North Korea.

Rajiv Shah, the head of the U.S. Agency for International Development , was quoted last week saying the United States will not send food aid until it receives adequate guarantees from North Korean officials that any aid will not be diverted to prop up the government.

But the relief groups, which helped deliver $3 million worth of U.S. flood assistance to North Korea this month, said the supplies were distributed directly to civilians.

The United States sent a team of experts to assess the food requirements in North Korea earlier this year. Similar teams have visited from the European Union and the United Nations, both of which said assistance is urgently needed. But a U.N. appeal for donations has fallen far short of the organization's target.

The organizations issuing the latest statement are Mercy Corps, World Vision, Samaritan's Purse, Global Resource Services and Christian Friends of Korea.

The groups say their members witnessed severe storm damage during their visit this month and that without immediate intervention, there is a risk of a far greater crisis in the next six to nine months.

North Korea has chronic problems feeding its population. Hundreds of thousands are believed to have died in a famine in the 1990s.