A peace deal to end 20 years of war in Sudan may not be signed this week as previously announced, a senior government official has said.
The 20-year civil war has caused untold misery
The United States is pressing both sides to reach a deal by 31 December.
But the delegate at the talks in Kenya, told the BBC that resolving issues on the three disputed regions is "proving to be a nightmare".
The war, pitting the Christian and animist south against the mainly Muslim north, has left some 2m people dead.
Sudan's President Omar al-Bashir has also suggested the 31 December deadline may be missed, but said a deal will be reached "within a week".
The government and the rebel Sudan People's Liberation Army (SPLA) last week reached an agreement to share oil resources, which had been one of the key issues.
They have also agreed to set up a joint army.
SPLA leader John Garang and the government's first vice president, Osman Ali Taha, on Monday continued their talks in the Kenyan resort town of Naivasha.
The status of three regions
But the government delegate said the debate on the disputed regions is slowing down the pace of the talks.
Both sides claim the regions of Abyei, Nuba mountains and the Southern Blue Nile.
Under a previous agreement, the south will be autonomous for six years, after which a referendum will be held on whether it should become independent.
The two parties are yet to begin negotiations on power sharing, yet another key issue before the comprehensive deal can be signed.