The United States is calling on South Africa to help prevent a humanitarian crisis in Sudan.

The U.S. special envoy to Sudan, Princeton Lyman, said civilians in South Kordofan and Blue Nile states are running out of food. During a conference in Pretoria Wednesday, he urged South Africa to pressure the Khartoum government to allow international aid groups access to the area.

On Tuesday, the U.S. issued a similar warning to members of the U.N. Security Council in a letter obtained by VOA.

The letter accuses Sudan of preventing aid groups from accessing the two states, where the government has been fighting rebel groups since the middle of last year.

It said that without substantial new aid to South Kordofan and Blue Nile, food security will deteriorate by March to an “emergency” level and eventually to famine conditions.

Sudan's ambassador to the U.N. said Tuesday that the humanitarian situation in both states is “normal” and that Sudan is not impeding access.