South Sudan accused former foe Sudan of holding 35,000 Southerners as \"slaves,\" stalling talks to resolve to furious oil dispute as tensions remain high between the two neighbours. \"There is unfortunately a disagreement, because the government of Sudan refused the inclusion of the freedom of about 35,000 South Sudanese enslaved citizens,\" South Sudan\'s chief negotiator Pagan Amum said. Amum said the abductees were taken hostage during Sudan\'s bloody 1983-2005 north-south civil war which ended in a peace deal that paved the way for South Sudan\'s formal independence in July. Thousands of South Sudanese were allegedly abducted by pro-government militia forces during the war and forced to work in the north, claims rejected by the government in Khartoum. The rivals are in the Ethiopian capital holding the latest round of dragging African-Union led talks. The two countries have been at loggerheads since the South broke away, threatening to reignite conflict between the two former bitter enemies. Oil has been a major sticking point in the talks, since Juba took 75 percent of Sudanese oil at independence but Khartoum controls processing and export facilities. But deals must also be made on contentious nationality issues, as well as border demarcation and the future of the contested Abyei region, claimed by both sides but occupied by Khartoum\'s army. Juba took the drastic decision to halt crude production in January, despite oil making up 98 percent of its revenue, after Sudan started seizing its shipments in lieu of a deal on transit fees. Khartoum said the approach from South Sudan was \"not constructive\" and proposed the creation of a separate high level committee to deal with the sticking points on nationality issues. However, Sudanese negotiator Sabir Mohamed al-Hassan said the talks were stalled because the South insisted on hammering out details about the proposed committee, including how citizens would be repatriated. \"They insisted to go into detail and we refused to go into detail, and the meeting broke down,\" he said. Some 500,000 South Sudanese remain in Sudan, and Khartoum has given them until April 8 to leave or regularise their status. However, the United Nations has said it is logistically impossible to repatriate all within the timeframe. Under South Sudanese law any Southern ethnic group member, or with ancestors born in the south, is eligible for nationality. \"That is why we thought it would be important to set up this committee as soon as possible because on the 8th... if there is not agreement, definitely there will be complications,\" Hassan added. Hassan admitted a deal is unlikely to be reached before this round of negotiations close on March 16. \"It takes two to tango. Personally, me... I\'m not really optimistic,\" he said.