Heavily armed attackers have killed 13 herders in a series of four cattle raids near Akobo town in Upper Nile State of southern Sudan during the past one week, a source in the area said.

Members of the Muerle ethnic group attacked Nuer-Lao cattle camps in various locations around Akobo on the Ethiopian border, David Lochhead, a Sudan analyst visiting Akobo said.

The victims included five men killed in nearby Ogalo, two people murdered during a raid at Brumath and four children killed in an attack on Pagay. Two other men were shot in a cattle camp east of Akobo. About 21 members of the Nuer-Lao community were wounded and hundreds of heads of cattle taken. It was not immediately clear how many casualties there were among the Muerle.

"All these attacks took place in the context of cattle raids, which intensify at the end of the dry season when all the cattle is in cattle camps," Lochhead said.

During the end of the dry season, local water sources dry up and various Sudanese ethnic groups, including the Nuer-Lao, Nuer-Jikany and the Muerle, drive their cattle towards the Sobat and Pibor rivers, in the vicinity of Akobo. The seasonal concentration of cattle and armed groups in a small area often results in increased tension and inter-ethnic fighting.

"The Muerle seemed well-supplied with ammunition and outgunned the cattle keepers," Lochhead added. "The Nuer-Lao didn't retaliate as they knew they wouldn't stand a chance," he said.

The Muerle are said to have been armed by the Sudanese forces during the 21-year civil war that pitted the government against rebels of the Sudan People Liberation Movement/Army. The war ended with the signing of a peace agreement in January 2005.

It was unclear whether the superior firepower of the Muerle was from old stocks of weapons or whether they had recently been re-supplied by elements within the Sudanese military who might be trying to sabotage the peace deal.

"This seemed like genuine cattle raiding," said Lochhead. "In the past, Muerle attacks were more militarised, and they would use mortars and rocket-propelled grenades when attacking villages."

The United Nations Mission in Sudan on Thursday evacuated by helicopter 10 people who sustained gun-fire inflicted fractures. They underwent surgery in Malakal, the capital of Upper Nile state.

Lochhead feared that without a settlement, the fighting could continue well into the rainy season - until the Muerle had moved south towards their rainy season pastures.

"The rainy season starts in a few weeks, so the fighting should subside by the beginning of June," Lochhead said.

[ This report does not necessarily reflect the views of the United Nations ]