Clashes between the southern army and a rebel militia group in south Sudan's Upper Nile state have left more than 40 people dead, including seven soldiers, southern army spokesman Philip Aguer said on Monday.
"There was fighting on Sunday between the SPLA and a former militia group under Ulony, a militia commander who had been in the service of Khartoum for a long time," the spokesman for the Sudan People's Liberation Army told AFP.
The militiamen attacked a group of SPLA soldiers who had gone to the market in Owach, a town west of Upper Nile's state capital Malakal, killing one and wounding one, Aguer said.
"After that incident, the SPLA attacked their camp at around 12:00 pm, and fighting took place in which 37 of Ulony's men and seven SPLA soldiers were killed, including the one that died earlier," he said, adding that another 28 soldiers were wounded.
Sources in Malakal confirmed that there had been fighting in Owach, but disputed the casualty figure given by Aguer.
"It's not as high as 40. I think between 13 and 15 people were killed altogether," said Susan Oyach, an assistant in the Upper Nile governor's office, adding that the situation was now calm.
Aguer said the army had recovered 37 AK-47 assault rifles, which had "definitely" been supplied by the north.
Northern army officials were not available to respond to the accusations.
The SPLA spokesman said Sunday's attack came despite the southern government allowing Ulony's group to join the army as part of president Salva Kiir's amnesty offer to rebel fighters in October.
Relations between north and south Sudan seemed to have improved during January's referendum on southern independence, but a string of deadly attacks by rebel militias in Upper Nile and neighbouring Jonglei state since last month has sparked a war of words between the two sides.
In the worst incident, more than 200 people died in an attack on SPLA soldiers by troops loyal to renegade southern general George Athor in northern Jonglei on February 9.
Juba has accused the rebels of acting on behalf of Khartoum in an attempt to destabilise the south, a charge northern officials have denied.
During the devastating 1983-2005 civil war between north and south Sudan, Khartoum armed militias among southern ethnic groups opposed to the southern Sudan People's Liberation Movement, which has repeatedly accused the northern authorities of maintaining the policy in a bid to destabilise the region.
Khartoum has in turn accused the southern authorities of backing rebel groups in the western region of Darfur, something they deny.
Analysts have said that maintaining security in the fledgling southern nation, which is due to achieve full independence in July, and disarming its civilian population, will be major challenges for the Juba government.