Sudan's south voted to separate from the north in a January referendum promised under a 2005 peace accord that ended decades of civil war. The underdeveloped region, the source of most of Sudan's 500,000 barrels per day of oil, has been beset by violence which has killed hundreds since the vote.

Twenty southern army soldiers were killed on Tuesday in a clash in the oil-producing Unity state with fighters loyal to Peter Gadet, a former senior southern army (SPLA) officer who rebelled this month, the military said.

"They (the rebels) overran a village in Mayom country. They burned it to the ground before the SPLA chased them off," said southern army spokesman Philip Aguer.

Two drivers were also killed when two civilian trucks hit landmines in the same county, Aguer said.

The rebels fought alongside Misseriya tribesmen from the north, Aguer said.

Southern leaders have accused their former civil war foes in the north of arming the renegades to try and destabilize the region and keep control of its oil, charges Khartoum denies.

The Misseriya who drive their cattle south to graze during the dry season claimed sole responsibility for the attack.