* Both sides claim gains in Monday's fighting
* Sudan says South Sudan has backed rebels, south denies
* Volatile border region home to thousands who fought with south (Adds rebel group comment, background on the fighting)
KHARTOUM, Oct 31 (Reuters) - Sudanese rebels and government forces clashed in a town in a key oil-producing border state on Monday, Sudan's government and the insurgent group said, in an escalation in fighting that has raised tensions with the newly-independent south.
Fighting broke out between Sudan's army and rebels in the South Kordofan state in June, just weeks before the south split off into a separate country. Both sides have blamed the other for starting the clashes.
Both Sudan's army and the rebels claimed gains over the other during Monday's fighting in the town of Taludi.
Ahmed Haroun, South Kordofan's governor, said Sudan's military repulsed the attack, and accused South Sudan of backing the rebels.
"Hundreds of soldiers from the Sudan People's Liberation Movement (in South Kordofan) were killed during an attack on the city of Taludi this morning," he told reporters at a news conference by telephone.
A spokesman for the SPLA in South Kordofan, Qamar Dalman, said the fighting was not over and disputed the government's figures, saying just five SPLA fighters had been killed so far.
He claimed rebels controlled up to half of Taludi and had killed 273 government soldiers.
Neither of the reports could be independently verified.
Many of the rebels fought against Khartoum as part of the south's Sudan People's Liberation Army (SPLA) during a decades-long civil war, but were left in the north when South Sudan became independent in July.
FIGHTING EXACERBATES TENSIONS
The fighting has exacerbated tensions between Khartoum and its former civil war foes in South Sudan, who are still negotiating over how to manage the formerly integrated oil industry and other sensitive issues.
A spokesman for Sudan's army repeated claims that the rebels had received training in South Sudan. South Sudan's government was not immediately available to comment, but has previously denied accusations it is supporting the insurgents.
South Kordofan and Blue Nile -- both states on Sudan's side of the border -- and the disputed Abyei area saw heavy fighting during the civil war, and fresh clashes have broken out in all three this year.
The three areas are still home to tens of thousands of fighters that sided with the south during the civil war.
Khartoum has accused groups in those territories of trying to spread chaos along the border, while rights groups have accused Khartoum of trying to stamp out remaining opposition on its side of the border.
South Sudan seceded in July after voting to separate in a January referendum promised in a 2005 peace deal that ended what was one of Africa's longest-running civil wars.
(Reporting by Khaled Abdelaziz; Writing by Alexander Dziadosz)
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