Pressure mounted on South Sudan's warring parties Tuesday to reach a ceasefire to end weeks of bitter fighting and atrocities on both sides that have devastated the young nation. Thousands have been killed and half a million civilians forced to flee the fighting between troops loyal to President Salva Kiir and rebels allied to his sacked deputy Riek Machar. Deadlocked ceasefire talks in Ethiopia are being mediated by the East African regional bloc IGAD, trying to broker an end to a conflict where the United Nations says atrocities have been committed, including mass killings, sexual violence and widespread destruction. Fighting has spiralled into ethnic killings between members of Kiir's Dinka people -- the country's largest group -- and Machar's Nuer. Many fear the conflict has spun out of the control of the politicians who sparked it. But feeling the pressure Kiir lashed out against the UN, accusing it of wanting to create a "parallel government" and falling just short of naming the UN peacekeeping chief as co-president. His outburst came after UN Secretary-General Ban Ki-moon warned of a "growing number of violations" including attempts by government figures and troops to enter a peacekeepers' base to which thousands of civilians had fled. "If that is the position of Ban Ki-moon he should make it clear that he wants the UN to take over South Sudan," Kiir said in a speech Monday. An emergency regional summit of leaders planned for Thursday in Juba has een cancelled, but the same issues of striking a deal will be discussed at the African Union in Addis Ababa next week, South Sudan's foreign ministry spokesman Mayen Makol told AFP. AU Commission chief Nkozasana Dlamini-Zuma, who visited Juba on Monday, demanded that both sides end the "senseless killings... and end the humanitarian tragedy unfolding in their country". A draft IGAD ceasefire accord, seen by AFP and presented to peace delegates meeting in Addis Ababa, notes the "scale of human suffering... with great loss of human life", since fighting broke out on December 15. The ceasefire proposal specifically highlights that both sides must "refrain" from attacking civilians, including summary executions, use of child soldiers as well as "rape, sexual abuse and torture". Pardon or prosecution? Both sides would also have to "freeze their forces" in their positions and create aid corridors, as agencies warn of a growing humanitarian crisis in an already deeply impoverished nation. A separate draft deal urges Kiir to pardon and release 11 key political detainees, one of the key sticking points. Kiir, in a presidential address on Monday after government forces wrested back full control of Malakal, the last major settlement under rebel control, said that "presidential pardons and general amnesties shall be part of peace efforts". The recapture of Malakal, one of the main battlefields since fighting erupted and the key town in oil-producing Upper Nile, came just two days after government troops celebrated the retaking of Bor, capital of Jonglei state. In Bor, civilians recounted grim stories of how the rebels gang-raped and murdered sick patients in the town's hospital. The government's success in Malakal has opened up the possibility of a shift in ceasefire talks deadlocked for two weeks, with some suggesting Juba had been reluctant to strike a deal while rebels still held urban centres. Kiir on Monday made a direct appeal to his enemy Machar, while still warning that those guilty of crimes would be held "accountable for the atrocities they have committed." "I still call Riek Machar and his group to lay down their weapons and come back and participate in the building of our new nation," Kiir said. "Nobody will disown them for what they have done. We have a space in our hearts to forgive him and his people." Rebels are reported to remain powerful and in control of large areas of the countryside, and battles continue. IGAD includes Uganda as a key member, whose forces have a taken a role in the fighting in support of Kiir. Machar has demanded Kampala withdraw all forces, claiming Ugandan fighter jets have tried to kill him. In Addis Ababa, little progress was seen Tuesday. Rebel delegate Hussein Mar Nyuot said the government team was discussing "the issue of withdrawal of Ugandans."