* Three killed in clash in south Sudan

* Violence in the south has intensified this year

KHARTOUM, Aug 19 (Reuters) - Three people from an armed tribal group in south Sudan have been killed in a gun battle with the semi-autonomous region's army, officials said on Wednesday.

The incident took place on Tuesday in the south's oil-producing Unity State where some of the bloodiest fighting occurred in a 22-year war between the north and south.

The southern government, set up under the 2005 peace accord, has struggled with inter-tribal raids and counter-attacks between pastoralists, often with cattle theft at the core of the violence. This year fighting in some areas has intensified.

Unity State's Information Minister Andrea Kuong told Reuters that members of the Bul Nuer tribe were returning from a revenge attempt on the Mayen Jur Dinka clan in the neighbouring state when they were intercepted by the army.

"Three were killed and seven injured," he said, adding the situation was calm now.

An army spokesman, Malaak Ayuen, said the army was trying to police the border between the two states.

The area's disarmament chief, Charles Machieng, said five people, including at least one from a family attacked in their home, were killed when members of the Mayen Jur Dinka attacked the Bul Nuer three days ago.

This was believed to be the reason for the Nuer revenge attempt, Machieng said. A senior member of the army, Biar Ajang, confirmed the fighting and death toll.

The southern army has sent soldiers to particularly bloody areas and have begun civilian disarmament in Lakes State that will continue into other areas in the next months, Ayuen said.

But after the war, in which some southern tribal militias were sponsored by Khartoum, trust in the southern army is low and disarmament and policing efforts have turned bloody before.

Growing discontent at slow peace dividends and perceived political meddling by north Sudan are two reasons given for the killings. Unity State residents have complained they did not receive compensation for oil producing land seized in the war.

The discovery of oil in the south inflamed a war that was fought between the mainly Christian and animist south and the largely Muslim north. (Reporting by Skye Wheeler, Writing by Edmund Blair)

AlertNet news is provided by