Addis Ababa - South Sudan's warring rivals held peace talks Monday in a bid to broker a deal to end its civil war, hours ahead of deadline to avoid possible sanctions.President Salva Kiir and rebel chief Riek Machar met alongside regional presidents in Ethiopia, under intense diplomatic pressure to sign a deal by a Monday deadline, Kenyan President Uhuru Kenyatta said.But Kiir, who arrived in Ethiopia late Sunday said he had been "compelled" to join the talks, warned it would not be possible to sign a lasting or full peace deal until all opposition factions could join the agreement."A peace that cannot be sustained cannot be signed," Kiir said on Sunday. "You should sign something that you will enjoy. If it is signed today and then tomorrow we go back to war, then what have we achieved?"Kenyatta however was more optimistic, saying late Sunday that the talks were "on course to strike a deal".Tens of thousands of people have been killed in the 20-month civil war.Effective dealThe rivals met late Sunday, with talks breaking in the early hours of Monday morning, which negotiations expected to continue later in the day.Kiir initially said he would not attend talks, complaining it was not possible to strike an effective deal because rebel forces have split.South Sudan's civil war began in December 2013 when Kiir accused his former deputy Machar of planning a coup, setting off a cycle of retaliatory killings that has split the poverty-stricken, landlocked country along ethnic lines.The latest round of talks opened on August 6, mediated by the regional eight-nation bloc IGAD, the Intergovernmental Authority on Development, as well as the United Nations, African Union, China and the "troika" of Britain, Norway and the United States.As well as Kenyatta, regional leaders at the talks include host Ethiopian Prime Minister Hailemariam Desalegn, as well as Ugandan President Yoweri Museveni - who has sent troops into South Sudan to back Kiir - and Sudanese President Omar al-Bashir.At least seven ceasefires have already been agreed and then broken within days, if not hours in Africa's newest country, which broke away from Sudan in 2011.