Jan Pronk said the Sudanese Government was willing to negotiate in the Abuja talks on the crisis in the Darfur region, but the rebels proved more difficult.
Khartoum had become more cooperative and was still willing to talk to the rebels, Pronk said.
"I do have the impression that the government was quite forthcoming. They accepted the talks without any precondition. They've accepted the agenda, they accepted any venue," he added.
"The rebels were a bit more difficult - they had pre-conditions - but anyway they came. And at a certain moment, perhaps the rebels felt it was no longer necessary to negotiate," Pronk said.
Qutbi al-Mahdi, political adviser to the Sudanese president, blamed the new US draft resolution on Darfur for the rebels' stance.
He said it was designed to abort the "political accord" which the Sudanese Government and the Darfur rebels were about to clinch in Abuja, under the auspices of the African Union (AU).
Speaking to Aljazeera, al-Mahdi said the threat of sanctions had made the Darfur rebels dig in their heels.
The ongoing conflict has displaced
1.4 million people in Darfur
The Khartoum government has accused rebels of walking out on peace talks and setting major obstacles in negotiations.
Rebels have been refusing to disarm and are insisting on more control of the region's resources. They say the government refuses to disarm the Janjawid militia, but have themselves not been willing to discuss the matter, insisting it be scrapped from the agenda of the talks.
Sudan says the Janjawid have agreed to be garrisoned after negotiations and are being disarmed, but says the rebels want to maintain international pressure and the Bush administration wants to use the crisis as a campaigning tool for the upcoming elections.
Some reports also suggest that rebels have been involved in traumatising civilians, at times acting as the Janjawid, and faking rape videos.
Pronk said the Khartoum government needed to do more to rein in the Janjawid.
Pronk also said that events in Darfur could not be labelled genocide, saying it was too early to use the word.
"I feel that the word is being used too fast," he said.
The US has used the word to describe the situation in Darfur. But an EU fact-finding mission a month ago said it could not be called a genocide.
US Secretary of State Colin Powell
called Darfur's situation genocide
Pronk also said all avenues had to be exhausted before sanctions were imposed.
Oil sanctions might hit fuel supplies and harm efforts to get food to the people of Darfur, he said.
"Today it's not time for sanctions, it's time for pressure. If you use the threats with the sanction element or pressure, then I'm with you," he said.
Imposing sanctions would show that the international community had given up, Pronk said.
The talks held in the Nigerian capital with AU mediators were designed to end a 19-month conflict in Darfur, where an estimated 1.4 million villagers have been displaced.
Pronk was optimistic and said even though talks were halted on Friday, it should not be seen as the end of negotiations.
The AU has said that talks will resume in October.