JUBA: A South Sudan rebel general has split with former Vice President Riek Machar and rejected his plans to join President Salva Kiir in a transitional government, raising prospects of fresh conflict in the country.

Fighting broke out in the world's youngest country in December 2013 between forces loyal to Kiir and rebels allied with his former deputy Machar, reopening ethnic fault lines that pit Kiir's Dinka people against Machar's Nuer forces.

Kiir and Machar have signed several ceasefire deals, only to violate them within days. The factions resumed peace talks last week, under growing international pressure and the threat of further sanctions if an Aug. 17 deadline is not met.

In June, the regional IGAD East African bloc proposed a transitional government as part of a solution to the conflict, with a vice presidential post allocated to the rebels.

Peter Gatdet, who said he was dismissed as a rebel commander along with other generals in July, said in a statement seen by Reuters on Wednesday the he had decided to split with Machar and asked him not to join the transitional government with Kiir.

"We reject any peace agreement that includes President Kiir and Riek Machar in leadership of the transition government of national unity," he said in the name of other rebel generals.

"Therefore, any peace that he signs with the government of South Sudan will not be legitimate and will not be respected by SPLM/A-IO led by generals," Gatdet said.

Spokesmen from IGAD, Machar and Kiir were not immediately reachable for comment.

Gatdet, a leading field commander on both a U.S. Treasury Department sanctions list and a U.N. blacklist for his role in the unrest, said both Machar and Kiir should also be barred from the transition government and wait to fight the next election.

"If this should not be the case, we suggest that a military-led transition government comprising officers from both parties be formed until next elections are conducted," he said.

He added that he and other generals in the rebel SPLM In-Opposition had lost confidence in Machar and had stripped him of his leadership positions.

In late July, while on a visit to Ethiopia, U.S. President Barack Obama said South Sudan's warring factions may face more international pressure if they did not reach a peace deal by Aug. 17.

Options discussed by those leaders ranged from applying sanctions to sending in a regional intervention force.