JUBA - Fighting in South Sudan's Jonglei state, where tribal militia forces are reported to be marching on a rival group, risks spiralling into "outright ethnic conflict", European diplomats warned Saturday.



Local government officials report that Lou Nuer gunmen from northern Jonglei are heading south towards Pibor, an area of their rivals, the Murle.



Previous such attacks in the troubled eastern region have seen hundreds -- if not thousands -- of civilians killed.



The joint statement from European ambassadors in South Sudan said they were "extremely concerned about reports of Lou Nuer mobilisation and initial clashes with armed Murle youth in Jonglei."



South Sudan's rebel-turned-official army has also been fighting in the region to crush a rebellion since April 2011 led by David Yau Yau, who comes from the Murle people.



"This could further exacerbate an already critical humanitarian situation and lead to an outright ethnic conflict with dramatic consequences," the statement added.



It asked South Sudan's army to deploy forces "to protect the civilian population in an even-handed manner".



In earlier clashes, rights groups accused all sides of abusing and raping civilians.



UN peacekeepers must also "make every possible effort" to assess the extent of the fighting, the statement added, reminding the force of its "responsibility to protect civilians".



The UN force has troops posted in the region, but say they are "not in an immediate position" to confirm details about any clashes.



The reports echo attacks in December 2011, when some 8,000 Lou Nuer marched south killing and looting in what they said were reprisals for earlier attacks and cattle raids by Murle fighters.



The UN later estimated over 600 people were massacred, although local officials reported the figure to have been far higher. — AFP