Negotiators have proposed establishing a court to try possible genocide and war crimes in South Sudan, in the latest power-sharing peace proposal hoped to end a 19-month civil war.

Peace talks, led by the eight-nation East African IGAD bloc, have been taking place in Ethiopia almost as long as the war, resulting in at least seven failed agreements or ceasefires, all broken within days or even hours.

An IGAD draft "compromise agreement" proposes an independent hybrid court, set up in collaboration with the African Union and United Nations, able to try possible genocide, crimes against humanity and war crimes.

US President Barack Obama, who travels to Ethiopia on Sunday, is expected to push peace efforts in South Sudan.

The 77-page IGAD draft deal, released Saturday, proposes offering rebels the post of first vice president, alongside another vice president, and offering the government 53 percent of national ministerial seats and the rebels 33 percent, with other parties making up the rest.

However, in the battleground states of Jonglei, Upper Nile and Unity, the power-sharing ratio is reversed, with the rebels offered 53 percent of state minister jobs and the government 33 percent.

Civil war started in December 2013, when President Salva Kiir accused Riek Machar, who had been sacked as vice president, of attempting a coup.

It also proposes the setting up of a truth and reconciliation commission to investigate "human rights violations and abuses, breaches of the rule of law and excessive abuses of power."

All foreign forces -- notably Ugandan troops, who are backing Kiir -- would have to leave the country, while the capital Juba would be a demilitarised zone.

After the collapse of the last round of talks, mediators expanded involvement to create an "IGAD-plus" group.

It now also includes the United Nations, five more African Union nations from across the continent -- Algeria, Chad, Nigeria, Rwanda and South Africa -- as well as China and the "Troika", Britain, Norway and the United States.

The warring forces are due to renew talks on August 5, ahead of an August 17 deadline to sign a deal, the latest in a string of ultimatums.