KHARTOUM, April 17 (Reuters) - Fifteen people including 11 civilians have been killed in clashes between militia fighters in southern Sudan since Saturday, straining a deal that ended the country's north-south civil war, officials said on Monday.
The fighting is between rival factions of a southern militia group called the South Sudan Defence Forces (SSDF), which fought alongside Sudanese government forces during the 20-year civil war, the local officials said.
The peace deal, known as the Comprehensive Peace Agreement (CPA), signed by the Khartoum government and the former rebels of the Sudan People's Liberation Movement (SPLM), stipulated that militias either join the army or the SPLM's forces.
The war broadly pitted the Islamist Khartoum government against the SPLM and its allies, made up mainly of Christians and followers of traditional African religions. About 2 million people died during the war and 4 million were made homeless.
SSDF commander Paulino Matip signed a deal in January to incorporate his forces into the SPLM's southern army but another commander, Gordon Kong, has opposed the move.
Local officials have said differences between Matip and Kong over which side to ally with have sparked the clashes. SSDF officials have played down earlier clashes saying they were over local tribal differences.
"The people from Gordon Kong's faction attacked our position in Longchauk on Saturday and they managed to dislodge our forces," said Nhail Thak, a commander with the pro-SPLM faction.
Thak said his forces recaptured Longchauk, about 200 km (125 miles) north of Malakal in Upper Nile state, on Monday. He said four soldiers and 11 civilians, who were caught in the crossfire, were killed in fighting since Saturday.
Thirty-two people, including 17 civilians, were killed in five days of violence between the two factions last week. That fighting was centred around the towns of Nasir and Ulang in the same state, local officials had said.
A senior SPLM official said he had heard reports of fighting and civilian deaths.
"There is some fighting in the area ... (it) shows that some people are not serious about the CPA and (it) damages confidence between the two partners," said the SPLM official, who asked not to be named.
A U.N. official said investigators were looking into reports of violence in the area but could not immediately confirm its extent.