The authorities in South Sudan say at least 81 people have been killed during heavy fighting between armed civilians and soldiers carrying out a disarmament exercise.

With several million guns thought to be in the hands of civilians and clashes between rival communities common, disarming the population is a huge challenge for the unity government.

It was formed earlier this year following a deal to end a six year civil war.

A spokesman for the military in South Sudan said armed youths attacked an army camp at night twice.

Fighting between the two sides then went on for many hours. Amongst the dead were 55 soldiers.

The violence in Warrap State's Tonj county is a sign of how hard it is going to be to disarm civilians.

In a place where cattle are more important than cash, people want to protect themselves against the frequent raids by rival communities. As long as they feel that the state will not protect them it is likely to be hard to disarm them.

Last week a civil society group warned that if the disarmament is rushed without meaningful consultation, the insecurity could get even worse.