Fifty-seven people were killed in tribal clashes in South Sudan this week, most of them women and children. Another 53 people were wounded in the clash between the Lou Nuer and Murle groups in Jonglei state, thirteen of whom needed to be airlifted to safety.

Five adult women and two adult men had gunshot wounds and the remaining six patients were children under five, with beatings or gunshot wounds, Medecins Sans Frontieres (Doctors without Borders) said in statement.

Tribal fighting between the Lou Nuer and Murle has restarted in recent weeks in one of the most under-developed regions on Earth.

On Wednesday, armed members of the Murle ethnic group attacked three Lou Nuer villages in the north of the state, primarily targeting non-combatants. The raid followed an attack by about 6,000 Lou Nuer fighters on the Murle town of Pibor last week. Around 60,000 Murle people fled the town as the attackers burned down homes and stole thousands of cattle, the United Nations stated.

These were probably revenge attacks, government spokesman Barnaba Marial Benjamin told Reuters.

Earlier, Murle men attacked and killed 24 people in two villages in Akobo county, Jonglei. The exact number of people who have been killed in the most recent ethnic clashes is unknown, but likely exceeds 1,000.

“We have decided to invade Murleland and wipe out the entire Murle tribe on the face of the earth,” the Lou Nuer warned in a public statement.

The attacks have overwhelmed both the United Nations -- which has a battalion of combat-ready peacekeepers near Pibor -- and the South Sudanese army, who have not been able to stop the gangs of warriors. The government is sending in more soldiers and police officers, but so far they have not been able to stop the killing.

The U.N. troops are there but they are not fighting the fighters who entered the town, Rev. Orozu Lokine Daky of Pibor's Presbyterian Church told the BBC last week.

They are just trying to protect the city center only, the rest of the town is now under [the control of] the fighters... The situation is deteriorating. My own mother and my own sister are now missing. I don't know where they are. I assume they are dead, he added.

Circle of Violence

The newest nation in the world, South Sudan has been plagued by violence since its independence six months ago. Tribes with arms left over from the first and second Sudanese civil wars have fought bitterly and stolen cattle -- the area's main industry -- while the government of South Sudan continues to fight with its northern neighbor.

The conflict can be traced back over a century, and while a number of civil wars, genocides and ethnic battles have started and ended, violence in the country has been constant since the end of colonial-era in the 1950s.

Cattle rustling has been there since 1898, government spokesman Barnaba Benjamin Marial told The Associated Press. But in those days they were using spears and sticks. Now they have acquired a lot of weapons during the civil war and this has made the cattle rustling... much more damaging than anything else.

As the main source of income for these groups, cattle are a valuable commodity and their theft is not taken lightly. During the Lou Nuer's most recent attack, some 50,000 cattle were stolen from the Murle, who in turn has rustled back the cattle.

The government of South Sudan is supported by a tenuous agreement between the country's various ethnic tribes and is therefore considered to be reluctant to get involved in conflicts.