Jamal Muhammad Ibrahim told Reuters that media reports saying Sudan would welcome UN peacekeepers were untrue.
"This is not accurate. I don't know who made this statement. ... It has to come after an assessment by the Sudan government. If the need arises then Sudan may decide to do so. Otherwise no one has the right to impose foreign forces on Sudan," he said.
Western governments have called for the 7,000 African Union peacekeepers in Sudan's vast west to be replaced or taken over by a UN mission. The badly equipped, under-funded AU troops have been unable to end the fighting in the area the size of France.
The government of Sudan and the main Darfur rebel faction signed a deal on Friday to end three years of fighting that has killed tens of thousands of people and forced 2 million to flee their homes.
That agreement raised hopes Khartoum might now consider a UN deployment because Sudan had said in the past it would only do so after a peace deal with Darfur rebels.
"The situation is, after the signing of the peace accord, Sudan may look into any proposals to helping prevent tragedy," Ibrahim said.
"In this context if there is any possibility for UN forces to replace the African forces already in Darfur, this is the decision of Sudan and it is not going to be imposed on Sudan."
He gave no timeline for possible troop replacement. Sudan has also refused to allow a UN planning team into the country to assess needs on the ground.
The AU voted in March to extend its mission in Sudan until September 30, to break the impasse over transferring the operation to the United Nations.
Jan Egeland, the UN under-secretary for humanitarian affairs, began a trip to Sudan on Sunday to assess the situation in Darfur and refugee camps in neighbouring Chad.