Former Irish president Mary Robinson has called for justice for anybody guilty of human rights abuses in South Sudan.
Ms Robinson is part of a group of international statesmen and women known as the Elders and led by ex-UN general secretary Kofi Annan.
The organisation expressed outrage about the alleged widespread use of mass rape as a tactic of war in the conflict-riven African state.
Ms Robinson said: "The suffering in South Sudan should shame us all.
"It is an affront to civilised values and the longer the international community allows the conflict and human rights abuses to persist the weaker those values become.
"As Elders we stand in solidarity with the people of South Sudan and will continue to press for peace and justice."
The UK recently described the violence as genocide.
A UN report said the country was experiencing ethnic cleansing by mostly government forces and their allies as part of a bloody civil war.
It is one of the world's newest countries, in the centre of Africa, after voting to break away from Sudan in 2011.
The Elders were established by late South African leader Nelson Mandela to promote peace in global conflict zones.
Mrs Robinson is a former UN High Commissioner for Human Rights.
Other members of the Elders include former Finnish president Martti Ahtisaari who was awarded a Nobel Peace Prize for his work as a peace broker, including in Northern Ireland where he verified the IRA had decommissioned its arms.
Mr Annan said: "South Sudan is a young country but its people have been consistently let down by their leaders who have been unable or unwilling to move away from conflict and personal enrichment at the expense of the nation.
"Alleged war crimes and gross human rights violations committed by parties to the conflict, including the government and armed opposition groups, are prolonging the suffering of the people, and those who are responsible need to be held accountable."
Other members of the group are at a conference in Armenia as part of the Aurora Humanitarian Initiative.