Military officials in southern Sudan say fresh clashes in the oil-rich Upper Nile region killed 25 people, including a tribal chief and his family.

Authorities say the violence began Friday when heavily armed fighters attacked an ethnic Dinka village in Bony-Thiang, killing 20 civilians.

Military officials say Dinka villagers retaliated Saturday by attacking a Shilluk tribal settlement nearby, killing five people.

An army spokesman with Sudan's leading party, the Sudan People's Liberation Movement, accused a breakaway political party of arming the Shilluk villagers, as part of a northern-backed campaign to undermine a 2005 peace deal.

Spokesman Kuol Diem Kuol accused former Foreign Minister Lam Akol, who formed the breakaway party, Sudan People's Liberation Movement for Democratic Change or SPLM, in June, of arming the villagers.

Akol dismissed the claim.

Authorities in the south have accused Akol of receiving money and support from the northern-based National Congress Party of President Omar al-Bashir.

Southern officials accuse Khartoum of trying to spark conflict to derail the 2005 peace deal, under which southern Sudan became semi-autonomous.

Southern Sudan is scheduled to vote on independence in 2011.

Khartoum denies the charge.

Some information for this report was provided by AFP and Reuters.