South Sudan: Rebel Athor claims Oliny as new ally
At least 50 people have reportedly been killed in South Sudan clashes, as rebel leader George Athor claims a new militia has joined him.
Both Mr Athor and South Sudan's army say more than 50 people have died in clashes in Upper Nile State but each says most of the casualties were on the other side.
The claims have not been verified.
The increasing violence comes as South Sudan prepares to declare independence from the north in July.
An overwhelming majority of voters backed secession in January's referendum - part of a peace deal following decades of north-south conflict.
President Omar al-Bashir has said he accepts the independence of the oil-rich south.
His advisers deny southern claims that they are linked to Mr Athor's fighters.
"We hope the south will be strong - this will reflect stability in the north," Rabie Abd al-Atti, a senior official with Mr Bashir's National Congress Party, told the BBC.
But southern army spokesman Col Phillip Aguer said weapons and munitions had been seized from a militia led by a man called Oliny in Upper Nile state, which came from the north.
Mr Athor told the BBC that Mr Oliny's fighters had joined his rebellion.
He also said his forces had been attacked by the army in Jonglei State.
Fighting in Jonglei between Mr Athor and the southern army has reportedly left hundreds dead this year.
The BBC's James Copnall in Khartoum says Mr Athor's rebellion is one of the great challenges facing the southern authorities as they move towards secession.
If it is not stamped out quickly it may well encourage others to take up arms, our correspondent says.
Mr Athor was a senior member of the Sudan People's Liberation Army during the war against the north.
He turned renegade last April, claiming he was cheated out of victory in elections for the post of state governor of Jonglei.
Despite a ceasefire agreement in January, clashes broke out again in Jonglei in February.
Both Sudan and the South are reliant on their oil revenues, which account for 98% of South Sudan's budget. But the two countries cannot agree how to divide the oil wealth of the former united state. Some 75% of the oil lies in the South but all the pipelines run north. It is feared that disputes over oil could lead the two neighbours to return to war.
Although they were united for many years, the two Sudans were always very different. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest.
Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.
The health inequalities in Sudan are illustrated by infant mortality rates. In South Sudan, one in 10 children die before their first birthday. Whereas in the more developed northern states, such as Gezira and White Nile, half of those children would be expected to survive.
The gulf in water resources between north and south is stark. In Khartoum, River Nile, and Gezira states, two-thirds of people have access to piped drinking water and pit latrines. In the south, boreholes and unprotected wells are the main drinking sources. More than 80% of southerners have no toilet facilities whatsoever.
Throughout the two Sudans, access to primary school education is strongly linked to household earnings. In the poorest parts of the south, less than 1% of children finish primary school. Whereas in the wealthier north, up to 50% of children complete primary level education.
Conflict and poverty are the main causes of food insecurity in both countries. In Sudan, many of the residents of war-affected Darfur and the border states of Blue Nile and South Kordofan, depend on food aid. The UN said about 2.8m people in South Sudan would require food aid in 2013. The northern states tend to be wealthier, more urbanised and less reliant on agriculture.