The US envoy to Sudan has expressed deep concern for the two-year-old peace deal that ended the 20-year civil war in the country.
"Trust is being lost," says Andrew Natsios
Andrew Natsios said the atmosphere between the governments of north and south Sudan had become poisonous.
He said the Comprehensive Peace Agreement had to be addressed before the situation deteriorated further.
The CPA is seen as a key factor in achieving resolution of the conflict in the Darfur region.
At least 200,000 people have died and some two million forced from their homes during the four-year conflict in Darfur.
Talks between Khartoum and rebel groups over Darfur are scheduled to begin in the Libyan capital on 27 October, although on Saturday a key rebel leader threatened to boycott them.
Mr Natsios said it was hoped when the 2005 governmental peace deal was signed that the two enemies in war would be partners in peace.
But he said that had not happened and described the governments of north and south Sudan as opponents unable to resolve their differences.
Mr Natsios said: "We are deeply concerned with the health of the CPA. The important deadlines have been missed... and trust is slowly being lost."
He said tensions, particularly along the border areas where armed units confront each other, were rising.
Meanwhile, key rebel leader Khalil Ibrahim has threatened to boycott the Darfur peace talks if more than two rebel groups are invited.
Mr Ibrahim, head of the Justice and Equality Movement (Jem), said only his group, a united Sudan Liberation Army and the government should participate.
Since last year, Darfur rebels have split into as many as 12 factions.
Mr Ibrahim criticised the African Union and United Nations envoys - Jan Eliasson and Salim Ahmed Salim - as being ill prepared for the talks.
The BBC's Amber Henshaw says many fear the talks are doomed from the outset because the factions are not united and another key leader, Abdul Wahid al-Nur of the Sudan Liberation Army, is refusing to take part.