Powerful South Sudanese military commander Paulino Matip, a longtime rebel warlord turned army chief, has died in hospital in Kenya, officials said Wednesday.

"We have lost a champion of peace and reconciliation -- we will miss him," South Sudanese Information Minister Barnaba Marial Benjamin told AFP. "He was undergoing treatment in Nairobi. He was ill for a long time."

Matip, from South Sudan's oil-rich Unity state, led a fearsome guerrilla army faction of his Bul Nuer people during Sudan's 1983-2005 civil war, a conflict that ended in a peace deal that paved the way for the South's independence last year.

During the civil war he split his forces from the South's then-rebel Sudan People's Liberation Army (SPLA) to side with Khartoum.

He later switched sides again, and was instrumental in bringing key militia forces back to the SPLA under a 2005 peace agreement, ending up as deputy commander-in-chief of the SPLA -- now the official South Sudanese army -- second only to President Salva Kiir.

"He has made his personal contribution despite earlier differences that caused the split in the SPLA," Benjamin said. "He brought all the armed groups under his command into the SPLA to reunite."

War-ravaged South Sudan, the world's youngest nation, is struggling to rebuild and integrate numerous militia factions, but Benjamin dismissed fears that Matip's death could see factions break away.

"These people are pessimists. Reconciliation has gone very well, from 2007 up to now these rebel groups have come back. There will be no more splits within the SPLA," he said.

Matip's body will be flown back to South Sudan to be buried, he added.

No official announcement has been made as to who succeeds him within the army.