South Sudan is facing the threat of a famine on a bigger scale than that seen in Ethiopia in the 1980s, aid agencies have warned.

An acute shortage of food is threatening the lives of millions, at the same time as the country is mired in a civil war between government forces and armed rebels.

The conflict has sparked widespread ethnic violence between the country's largest tribal groups, the Dinka and the Nuer, and has led to more than one million fleeing their homes.

Stephen Sackur reports from Juba.