Nobel Peace Prize laureate Desmond Tutu on Sunday appealed for peace in troubled South Sudan, on the eve of the country's first anniversary.

Tutu was speaking to political, military and religious leaders from the world's youngest nation, where looming conflict with the rump state of Sudan and dim economic prospects cast a pall over celebrations.

"God wants to make South Sudan prosperous and peaceful," the 80-year-old retired South African archbishop said.

"Because of war, they say 40 percent of your people, four out of every ten, depend on food from outside," he said.

"We want to return to come again and celebrate your nationhood with you and see a South Sudan that grows its own food, and is eradicating poverty and ignorance," Tutu added.

Landlocked South Sudan, which relies on the infrastructure of the North to export its oil, decided to stop pumping crude barely six months after becoming a state despite it almost being its only source of revenue.

Juba, still reeling from over half a century of civil war, was angered to see Khartoum siphoning off its crude after a row over pipeline fees.

"Your oil is not flowing, and it's not God that closed the pipes — it's war. Stop the war, and the oil will flow," Tutu said.

Tutu was on a visit with two other senior peace negotiators — Finland Martti Ahtisaari and Ireland's Mary Robinson. The trio were expected in Khartoum later.