KHARTOUM: Sixteen people have been killed in clashes between south Sudan troops and cattle herders from the northern Messeria tribe in the southern Unity state, officials said on Saturday.

On Thursday, "the Messeria attacked at 6:00 pm a garrison of the SPLA," the former southern Sudan People's Liberation Army, in a village near Bentiu, capital of Unity, southern army spokesman Kuol Deim Kuom told AFP.

"On our side there are eight killed, including one civilian and 11 injured ... We have found eight bodies of Messeria on the battlefield ground," he said.

"It was a planned attack. There are hidden forces that support them," Kuol said.

The southern army regularly accuses the central government in Khartoum of arming tribes or militias in order to destabilise south Sudan ahead of a January 11 referendum on its independence.

Cattle herders from the nomadic Arab Messeria tribe are based in the north of South Kordofan state, but move around to feed their cattle. Their traditional route goes right into the contested region of Abyei on the border between north and south Sudan, and even into south Sudan.

After the end of a decades-long civil war between north and south Sudan in 2005, southern officials began a disarmement campaign and asked the Messeria not to cross the Bahr Al-Arab region on southern territory.

In 2009, some 2,500 people were killed and 350,000 fled their homes -- a higher death toll than in the troubled western region of Darfur.