By David Lewis

ABYEI, Sudan, May 15 (Reuters) - Thousands of civilians fled clashes between Sudan's former north-south civil war foes in the oil-rich central town of Abyei on Thursday, local officials said.

The clashes, sparked by a local dispute, have highlighted the tension in an area claimed by both Khartoum and South Sudan. More than three years after a 2005 peace deal, they have not agreed on borders or a local government for the region.

Sporadic gunfire could be heard on the second day of clashes and smoke rose from the town.

"Most of the civilians have left town. There are about 25,000 east of Abyei," said Malony Tong, a local official from the former southern rebel Sudan People's Liberation Movement (SPLM). "It is not calm".

Around 50 civilians sought refuge at the gates of the U.N. peacekeeping compound but were not allowed to enter. International U.N. staff were being evacuated.

Tensions have been high for months between South Sudan and Khartoum over delays in implementing the 2005 peace deal. Both sides blame the other for stalling.

The SPLM says more than $1 billion in oil revenues from Abyei has been taken by the ruling National Congress Party rather than shared with the south as the peace deal prescribes.

But despite the clashes in Abyei, north-south relations have improved markedly since an unprecedented attack by Darfur rebels on Khartoum at the weekend when South Sudan offered military help to the government.

The 2005 peace deal did not cover Sudan's western Darfur region, where war broke out in 2003.

Sudan has suffered decades of conflict between Khartoum and far-flung regions that complain of neglect and discrimination by the traditionally Arab-dominated central government.

Clashes along the north-south border have continued despite the 2005 accord and have killed hundreds of people in the past year. A lack of discipline by ex-rebels and pro-Khartoum militias means fighting can easily flare.

Some 2 million people died in the war between north Sudan and the largely Christian and animist south.

International experts believe 200,000 have died as a result of the war in Darfur, where Muslim but non-Arab Darfuris took up arms in 2003. The government says only 10,000 people have been killed there.

The Darfuri Justice and Equality Movement brought the regional conflicts to the capital for the first time on Saturday in the attack which killed more than 200 people. Sudan blamed Chad for the assault and cut diplomatic relations.

The Greater Nile Petroleum Operation Company (GNPOC), a consortium led by the Chinese CNPC <0135.HK>, India's ONGC <ONGC.BO> and Malaysian Petronas [PETR.UL] works in Abyei. Experts say oil production had declined in the past few years.

(Writing by Opheera McDoom; Editing by Matthew Tostevin)

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