At least 13 people have been killed and a number of others injured in clashes between the Sudan People's Liberation Army (SPLA) and northern Misseriya nomads.

The clashes broke out on Wednesday in the volatile oil-producing Unity state close to the north-south border. Two southern soldiers and 11 nomads were killed.

The south Sudan's army says the situation is now under control.

This comes ahead of the country's first presidential and legislative elections in 24 years, scheduled to be held in April.

The army says political rivals in the north are encouraging tribal violence in order to hamper national elections.

According to the UN, up to 400 people have been killed and thousands have fled their homes this year as a result of the violence in south Sudan.