JUBA, Apr 22, 2011 (AFP) - South Sudanese rebels in key oil-producing Unity state threatened Friday to launch more attacks after a three-day offensive forced 130 industry workers out of the volatile region.

However, officials and military in the soon to be independent south dismissed the rebels' claims, saying the offensive had been defeated and that northern oil workers would soon be able to return.

Rebels led by former southern army general Peter Gadet said they had taken the small town of Mankien and were attacking the county headquarters of Mayom.

"We destroyed at least five army vehicles, but have also captured nine in good condition, making us more mobile," said rebel spokesman Bol Gatkouth, a former lawmaker in the south's parliament.

"We will not stop this attack and will continue fighting," he added, rejecting army claims the fighters had suffered "heavy casualties."

"We have some casualties, but they are not too many, it is not affecting our force," said Bol. "Indeed we are gaining more recruits."

It was not possible to independently confirm the claim, while the army insisted the rebels had been pushed back from the remote settlement.

"The rebels attacked the town of Mankien on Thursday, and fighting continued until the evening," said Philip Aguer, spokesman for the south's Sudan People's Liberation Army.

"However, the SPLA counterattack pushed the rebels out -- they are simply lying when they say they are in control," Aguer added. "There were casualties but we still do not have details from the field."

At least 130 northern oil workers had been transferred to South Kordofan state, across the north-south border, due to security concerns from the fighting, according to Unity state information minister Gideon Gatpan.

"The workers went to the headquarters in Heglig oil field because there were fears they could be in danger," said Gatpan.

"However, as soon as the security situation returns to normal they are free to return, and we expect that to be very soon."

The oil ministry confirmed the northern workers had been moved to the north and said it did not know how much the clashes had affected Unity's crude production, which averaged about 80,000 barrels per day in the past three months.

"All of the northern oil workers have been evacuated," Azhari Abdullah, the ministry's head of exploration and production, told AFP.

"The non-essential staff have already been transferred back to Khartoum, and now they are in the process of going back to Heglig. The essential staff stayed in Heglig.

"I don't know how much this has affected production. That is what we want to find out," he added.

This week's clashes were close to the still disputed north-south border, as well as the flashpoint Abyei region.

The fighting began when the militia group, who call themselves the South Sudan Liberation Army (SSLA), blew up two civilian tankers using land mines on Tuesday, before storming an army outpost, killing at least 20 soldiers.

They later abandoned the village before army reinforcements retook the position.

Earlier this month, the rebel group said it planned to overthrow the southern government, denouncing the "rampant corruption" at the top levels of the SPLM, the south's ruling party.

The SPLM has repeatedly accused Khartoum of arming splinter militia groups like Gadet's to destabilise the south ahead of its secession from the north in July, a claim Khartoum rejects.

The UN warned this week military tensions and political disputes pose a new threat to Africa's biggest nation, which is due to split in two in July after the south voted overwhelmingly for independence in a January referendum.

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Copyright AFP 2011.