KHARTOUM (AFP) - Rival Sudanese forces resumed heavy fighting on Tuesday in Abyei, the flashpoint oil-rich border area between north and south whose status remains contested three years after the end of civil war.

Fighting raged for at least five hours between government troops and southern ex-rebels, who fought a 21-year civil war until reaching a power-sharing peace agreement with Khartoum in 2005, aid workers told AFP.

 

The clashes, involving gunfire and mortar rounds, reached just outside the gate of the main UN compound on the edge of town and severed a tentative ceasefire brokered by the United Nations late last week, they said.

The southern Sudan People's Liberation Army (SPLA) attacked the impoverished town of Abyei, which lies at the heart of the contested border region rich in oil and which had been under government military control, they said.

"It started at 4:00 am (0100 GMT) and stopped around 8:00 am. It started again just before 10:00 am and lasted about an hour. The fighting has been very heavy," said one aid worker on condition of anonymity.

"It's currently quiet but I think the general feeling is that this is not the end."

Fears are rising of a possible counter-attack on Agok, 25 kilometres (16 miles) south where UN agencies and aid workers are distributing food to some of the 30,000 to 50,000 people displaced by fighting in Abyei last week.

"The UN is currently using all means we can to get this resolved peacefully," Chris Johnson, head of the UN mission in Abyei, told AFP.

SUNA, the state news agency in Khartoum, said SPLA forces attacked Abyei at dawn using heavy artillery.

The violence erupted one day after UN agencies and aid workers further to the south began distributing food to some of the 30,000 to 50,000 people displaced by deadly fighting last week that levelled the marketplace in Abyei.

The United Nations had warned Monday that continued insecurity posed challenges to humanitarian relief efforts in the west.

The world body last week evacuated its entire civilian staff from the town following days of fighting between government forces and the SPLA.

Almost the entire population of the impoverished settlement in the heart of an oil-rich district claimed by both north and south are believed to have fled the fighting.

Casualty figures are not clear. Aid workers and south Sudan politicians have reported bodies in the streets and looting in the ramshackle town.

Impasse over the area -- whose oil wealth is bitterly contested by the two sides -- is one of the main stumbling blocks delaying implementation of the January 2005 peace deal and exacerbating tensions between north and south.

In 2011, Abyei will hold a referendum on whether to retain its special administrative status in the north or be incorporated into the south.

A second referendum on whether the south should break away as an independent state is also to be held.