UN Secretary General Ban Ki-moon has called for a special tribunal for South Sudan, saying there are grounds to believe that crimes against humanity have been committed since widespread violence began five months ago.
The UN chief welcomed on Monday the ceasefire agreement signed by President Salva Kiir last Friday with his former vice president, Riek Machar, and demanded an immediate end to fighting, which flared over the weekend.
He called for "30 days of tranquillity" so farmers can plant crops in peace to avoid famine in the world's newest nation.
"If the conflict continues, half of South Sudan's 12 million people will either be displaced internally, refugees abroad, starving or dead by the year's end," Ban warned the UN Security Council, the AP news agency reported.
Kiir fired Machar last July and accused him of trying to oust him in a coup in December, which sparked months of ethnic attacks and killings.
Fighting took place between troops loyal to Kiir, an ethnic Dinka, and those loyal to Machar, an ethnic Nuer.
Ban, who visited South Sudan last week, said that since the crisis began, "many thousands of South Sudanese have been killed, atrocities have been committed by both sides, more than a million people have been displaced and nearly five million more need humanitarian assistance."
'Atrocities by all sides'
A UN report last week said gross violations of human rights had been committed "on a massive scale" in South Sudan.
Ban said that report "underscores the level of atrocities committed by all sides" and "a special -or hybrid- tribunal, with international involvement should be considered."
UN human rights chief Navi Pillay said after meetings with Kiir and Machar last week that she had warned them "they will inevitably be the subject of international investigations regarding the extent of their knowledge of war crimes and crimes against humanity committed by subordinates under their authority," and their failure to stop it.
Ban said his message to both leaders "was quite clear and loud that we have found crimes against humanity by both sides" and the perpetrators must be held accountable, AP reported.
Francis Deng, South Sudan's UN ambassador, who was Ban's special adviser on the prevention of genocide, told the council his country "has been experiencing one of the worst atrocities the world has seen in the last decades".
He expressed hope that "the specular accomplishment" of Ban and US Secretary of State John Kerry in getting Kiir and Machar to meet face-to-face "will usher South Sudan to a renewed commitment to peace, security, stability and dignity for all its people".