VATICAN CITY (Reuters) - The Vatican brought together South Sudanese leaders for 24 hours of prayer and preaching on Wednesday, a last ditch attempt to heal bitter divisions a month before the war-ravaged nation is due to set up a unity government.

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The retreat, which a Vatican statement called “both ecumenical and diplomatic”, will end on Thursday with an address to the leaders by Pope Francis, who has expressed a desire to visit South Sudan.

The leaders are all Christians, including President Salva Kiir, his former deputy turned rebel leader Riek Machar, and three other vice presidents.

Machar’s presence was in doubt until the last minute because aides said that Sudan, which is a guarantor to the September peace deal, has been restricting his movements in capital, Khartoum.

Sudan, which is predominantly Muslim, and South Sudan, predominately Christian, fought each other for decades before the south became independent in 2011.

Oil-rich South Sudan plunged into civil war in two years later after Kiir, a Dinka, fired Machar, from the Nuer ethnic group, from the vice presidency.

Brutal fighting broke out, characterized by extreme sexual violence, the use of child soldiers and attacks on civilians along ethnic faultlines. About 400,000 people died and more than a third of the country’s 12 million people were uprooted, sparking Africa’s worst refugee crisis since the 1994 Rwandan genocide.

Machar landed in Rome about an hour before the retreat was due to start in the Pope’s Vatican guest house. The leaders will live there and eat together during the retreat.

Also attending are the Archbishop of Canterbury, Justin Welby, the spiritual leader of the worldwide Anglican communion; members of the South Sudan Council of Churches; and other African Catholic and Presbyterian Church leaders.

Welby had proposed the retreat to the pope.

A Vatican statement said the retreat would offer the leaders “a propitious occasion for reflection and prayer, as well as an occasion for encounter and reconciliation”. An African Jesuit, Father Agbonkhianmeghe Orobator, will preach.

The two sides signed a power-sharing deal in September calling on the main rival factions to assemble, screen and train their respective forces to create a national army before the formation of a unity government.

That has not happened. Instead, the government has dismissed U.N. investigations into war crimes and gang rape and asked for $285 million in funding to implement the deal.

Last month, Brussels-based think-tank the International Crisis Group warned the deal risks total collapse before May 12, when the leaders are due to start sharing power.