* Unity state expelled northern workers after clashes
* Production disrupted at 84,000 bpd oilfields
* Fresh fighting between rebel militia, S.Sudan army
(Clarifies Deng's title in paragraph 1, 3)
KHARTOUM, April 21 (Reuters) - South Sudan's government has decided to re-admit northern oil workers expelled from the oil-producing Unity state after deadly clashes in the region, the Sudanese petroleum minister said.
Unity state on Wednesday kicked out north Sudanese working in its oilfields after accusing Khartoum of backing rebel militias fighting the south Sudan army. A clash on Tuesday between the two sides killed at least 31 people. [ID:nLDE73J233]
Output at the Unity oilfields, which produce 84,000 barrels per day, was disrupted for a day after the expulsion since most of the 212 workers there were north Sudanese, Sudan's Petroleum Minister Lual Deng, a southerner, told Reuters by phone.
The decision to throw out the northern oil workers was outside the jurisdiction of the governor and was overturned by South Sudan's president, Deng said. However, some of the expelled oil workers had returned to Khartoum and data on Thursday's production was not immediately available, he said.
Mangar Amerdid, a spokesman for south Sudan President Salva Kiir, said he could not confirm the move by the president. However, Unity State's information minister has advised that it had been removing oil workers for their own safety, not as a retaliation aginst the north, Amerdid said.
Sudan's south voted to separate from the north in a January referendum promised under a 2005 peace accord that ended decades of civil war in Africa's largest country, with the formal breakaway set for July 9.
The underdeveloped region, the source of most of Sudan's 500,000 barrels per day of oil, has been beset by violence that has killed hundreds since the referendum.
Analysts say South Sudan will have to maintain security to avoid becoming a failed state that destabilises the whole region.
Southern leaders have accused their former civil war foes in the north of arming the renegades to try and destabilise the region and keep control of its oil, charges Khartoum denies.
The news came as fighting broke out between rebel militia and the south Sudan army in the same county in Unity state where they battled on Tuesday, the southern army said.
Misseriya Arab nomads from the north claimed sole responsibility for Tuesday's attack. But the southern army (SPLA) has said they fought alongside fighters loyals to Peter Gadet, a former SPLA officer who turned renegade.
The latest fighting was also between rebel SPLA soldiers who had banded with the Misseriya under Gadet and the southern army in Mayom county, southern army spokesman Philip Aguer said.
"This is their second wave of attacks," Aguer said. He said there were no confirmed casualties yet.
(Reporting by Deepa Babington in Khartoum and Jeremy Clarke in Juba; editing by Mark Heinrich)
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