South Sudan's food crisis 'worst in the world' - UN

The BBC's Rob Broomby: "The UN says it's the worst food crisis in the world"

It said there was a "catastrophic food insecurity" in the country, urging donor nations who pledged $618m (£364m) in aid to make good on their promise.

The UN children's fund, Unicef, said some four million - a third of the population - could be affected.

It said that 50,000 children may die of hunger in the conflict-torn country unless international help increased.

More than a million people have fled their homes since fighting erupted between different factions of South Sudan's ruling party last December.

Thousands have now died in the conflict that started as a political dispute between President Salva Kiir and his deputy Riek Machar but has since escalated into ethnic violence.

Months of fighting have prevented farmers from planting or harvesting crops, causing food shortages nationwide.

The onset of the rainy season has added to the problem, dashing hopes that displaced farmers plant crops to feed themselves in the future, the BBC's Rob Broomby reports.

South Sudan, which gained independence from Sudan in 2011, topped the list of fragile states in this year's index released by The Fund for Peace, a leading US-based research institute.