At least 56 combatants were killed in clashes between militia fighters and soldiers in South Sudan's Upper Nile state, just four months before the region is due to become independent.

Philip Aguer, a spokesman for the southern SPLA army, said militia fighters killed two southern government soldiers on Sunday morning, and in an army counter-attack, 47 militiamen and seven soldiers died.

South Sudan is expected to secede on 9 July after southerners overwhelmingly voted to declare independence from Khartoum in a referendum in January – a vote promised in a 2005 peace accord that ended decades of civil war between North and South.

Mr Aguer accused Sudan's northern government of arming militias to try to disrupt the region and said there were signs that Khartoum-backed attacks were escalating.

No one was immediately available to comment from North Sudan's dominant National Congress Party, which has dismissed similar accusations in the past.