The United Nations is warning that famine could again threaten millions of people in southern Sudan next year, unless the government and rebels agree to extend a partial ceasefire in the country's long running civil war.

The UN's Operation Lifeline Sudan says despite millions of dollars of aid, the food situation remains fragile.

A six month old ceasefire, which applies only to the worst affected area of Bahr el Ghazal, is due to expire on January 15.

Rebels from the mainly Christian south have been fighting the largely Arab and Muslim north since 1983 in a civil war which is believed to have cost over a million lives.