South Sudan, which voted in a January referendum to become an independent state, formally ending decades of conflict with the north, has seen a surge of rebel and tribal violence, marring the celebrations ahead of the secession.

Analysts warn that the underdeveloped south, due to split away in July, could become a failed state and destabilize the whole region if security deteriorates further.

More than 1,100 people have been killed in tribal and rebel violence in south Sudan so far since the referendum, according to official figures.

The southern army (SPLA) launched an attack on a rebel militia led by former SPLA officer Peter Gadet in the oil-producing Unity state Sunday, the state's Information Minister Gideon Gatpan Thoar said.

Reuters