Sudan and former southern rebels agreed here to accept as binding an arbitration ruling due next month on a boundary dispute over the contested oil-rich Abyei region, US officials said Tuesday. The Sudanese government and the Sudan People's Liberation Movement (SPLM) reached the deal on Abyei before international talks opened in Washington to bolster a fragile Comprehensive Peace Agreement (CPA) between north and south. Both agreed to 'accept the Abyei arbitration as final and binding,' Scott Gration, the US special envoy for Sudan, told reporters in a conference call, adding both sides pledged to ensure the people on the ground also accept it. Four and a half years after the CPA ended what was Africa's longest-running civil war, the boundaries between north and south, and of the oil-rich Abyei area have yet to be finalized. The ruling on the Abyei demarcation is due July 18-22, a US official said. Several rival ethnic groups have clashed in the south in recent months -- violence that southern Sudanese president Salva Kiir, who is also Sudan's vice president, has blamed on unnamed outside and internal forces. Gration called for strong international support to help implement the CPA when he gave an opening speech at the gathering of 20 countries and more than a dozen international organizations at a Washington hotel. 'We must work together urgently to set the foundation for a future of peace and security in Sudan,' Gration told the gathering. 'The US cannot do it alone. All of this will depend once again on your efforts,' he added. 'But our time is short,' Gration told his audience, referring to a referendum on the south's future in January 2011. Agreements have to be secured on border demarcations, wealth-sharing and power- sharing. The CPA ended a two-decade civil war, the longest in Africa, that claimed 1.5 million lives. The deal offered the south a six-year transitional period of regional autonomy and participation in a unity government until the 2011 referendum on self- determination. Abyei will hold also hold a referendum the same year on whether to retain its current special administrative status in the north, or join the south. 