Officials in South Sudan say nearly 50 people have been killed in a revenge attack sparked by clashes between rival communities.

Authorities say the fighting began late Monday when armed men from the Murle tribe stormed a Lou Nuer village in Duk county, in the northern part of Jonglei state.

This is the second attack by the Murle on a Lou Nuer community in less than a week.

Officials say the attack was revenge for massive raids by the Lou Nuer tribe on Murle areas late last month.

About 6,000 men from the Lou Nuer attacked the town of Pibor and other areas controlled by the Murle in December. U.N. officials said at least several dozen people were killed.

South Sudan is the world's newest country but has been wracked with tribal violence and fighting between the government and rebel groups almost from the start.

The country is also trying to cope with an influx of refugees from neighboring Sudan and disputes with Khartoum over borders and oil revenue. The tension has raised fears of war in the region.