The United States says famine conditions are “likely” in two parts of Sudan unless the government allows aid groups to access the areas.

The warning is contained in a letter, obtained by VOA Tuesday, that the U.S. is circulating to members of the U.N. Security Council.

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

The U.S. says that without substantial new aid to the two states, food security will deteriorate by March to an “emergency” level, where people will be unable to meet basic food needs, and eventually to famine conditions, the most serious form of food crisis as classified by the U.N.

There has been no immediate reaction from the Sudanese government.

U.N. officials and international aid groups have sounded warnings about the situation in Southern Kordofan and Blue Nile. Tens of thousands of refugees from the states have poured into neighboring South Sudan.

The rebels in both states favor the south, which declared independence from Sudan in July.