Welby, who met with South Sudanese President Salva Kiir, arrived in Juba on Thursday as part of a four-nation African tour.

Thousands have been killed in the fighting pitting forces loyal to President Salva Kiir against a loose coalition of army defectors and ethnic militia nominally headed by sacked vice president Riek Machar, a seasoned guerrilla fighter.

The fighting has seen waves of brutal revenge attacks, with the United Nations and rights workers reporting that horrific atrocities were committed by both sides.

"I've heard particularly bad news of attacks....what is important is that... the facts of this are established in a way that no one can deny, and that we understand fully, and lessons are learned," Welby said. "There must be no impunity."

"In a world where everyone is used to killing, I ask you to call on all your courage and faith, to remember your suffering, to remember those who have been killed, to be clear that those were terrible injustices, but to pray that you may love your enemies," he said in a sermon in Juba.

Both sides implemented the ceasefire last Friday, but combat has only eased, not ended.

South Sudan: "We're a young nation and should be supported"

(AFP, VoR)