By Jeremy Clarke and Alex Dziadosz
JUBA/KHARTOUM (Reuters) - Clashes have broken out in a flashpoint region of Sudan controlled by the northern government, exacerbating tensions as the southern portion of the vast country prepares to secede following a referendum.
Two southern party officials and the United Nations reported fighting at the weekend in the Nuba region of South Kordofan, an area in northern territory that the Khartoum authorities have threatened to clear of southern-allied armed groups.
Tensions have been mounting between north and south Sudan ahead of the scheduled July 9 division of the country.
The Khartoum government seized the disputed Abyei region on May 21, causing tens of thousands of people to flee and drawing sharp international criticism.
In the latest violence, the United Nations said it had received reports of shooting in the village of Umm Dorain in South Kordofan Sunday and was sending military observers to gather details.
"There were reports of shooting in Umm Dorain, which took place late morning," spokeswoman Hua Jiang said.
Unknown armed groups also attacked a police station in the town of Kadugli late Saturday, taking some weapons before leaving, a spokesman for the U.N. mission in Sudan said.
Two officials with the southern ruling party in South Kordofan confirmed the clashes in Kadugli and Umm Dorain, and accused Khartoum of launching the attacks.
"NCP (National Congress Party) attacked this morning in Umm Dorain and yesterday night in Kadugli, but it is quiet now," an official with the southern ruling party, the Sudan People's Liberation Movement (SPLM), told Reuters.
The National Congress Party is the ruling party of the Khartoum government.
In statement carried by the state news agency SUNA, a spokesman for the northern army said "the incident" in Umm Dorain was an individual case resulting from one soldier firing at random.
"The situation was contained," the statement said, adding Kadugli was calm and that relations between Sudan's armed forces and "the other party" in the Nuba region were stable.
Analysts have said fighting could erupt in parts of South Kordofan and the north-run Blue Nile states, which are home to southern-allied armed groups that fought Khartoum during the civil war. Southern officials say the South Kordofan militia are northerners and so Juba cannot tell them to withdraw south.
Southerners voted overwhelmingly to secede in a January referendum promised by a 2005 Comprehensive Peace Agreement (CPA) that ended decades of civil war.
"The SPLM is still respecting the CPA and the international community, but if they attack again, no one will accept that, and we will be defending ourselves," the southern party official said.
He added that tanks were used, but did not give details. A second official said the northern army had shelled Umm Dorain. The reports could not be independently verified.
Both officials said they did not know if there had been any casualties yet.
The division of Sudan has been complicated by unresolved disputes including the exact position of the common border and the fate of Abyei, which is used all year round by the south-linked Dinka Ngok people and for part of the year by northern Arab Misseriya nomads.
Abyei is prized for its fertile grazing land, but also produces some oil, which Khartoum may be eager to hold on to as the south breaks away, taking with it some three-quarters of the country's oil revenues.
About 45 percent of Khartoum's budget comes from oil.
The occupation of Abyei followed an attack on a convoy of northern soldiers and U.N. peacekeepers that was blamed on southern forces.
Khartoum has refused calls from the United States, United Nations and southern officials to withdraw from Abyei, saying the land belongs to the north and its troops will remain until the dispute is resolved.
(Additional reporting by Khaled Abdelaziz; Writing by Alex Dziadosz; Editing by Jon Boyle)