Sudan's ruling party has rejected a draft United Nations resolution on sending peacekeepers to Darfur.
African Union troops are overstretched in Darfur
The plan would "impose complete tutelage" on Sudan, said National Congress Party chairman Ghazi Salah Eldin Atabani.
Shortly afterwards, it was announced a top US diplomat is to go to Khartoum to try to convince Sudan's government.
The UN and the African Union (AU) agree that the UN should take over the peace mission from the cash-strapped AU.
The US and the UK have circulated the draft, calling for 17,000 well-equipped peacekeepers, at the Security Council.
On Sunday, two AU peacekeepers were shot and killed in Darfur, the AU says.
"The draft resolution is worse than previous ones as it is an attempt to impose complete tutelage on the Sudan," Mr Atabani was quoted as saying after a meeting chaired by President Omar al-Bashir.
"Any state that sponsors this draft resolution will be regarded as assuming a hostile attitude against the Sudan," he said.
BBC Africa analyst David Bamford says as long as the Sudanese government opposes the plan for the UN to take charge, it is hard to see how the Security Council could bypass its objections.
President Bashir has sent a letter to the Council, saying Sudan needs more time to sort out Darfur by itself.
He has said he is sending in more Sudanese troops, but Darfur rebels say that government forces - far from pacifying the situation - have been operating in co-ordination with the Arab Janjaweed militia to prolong the war.
On Wednesday, the International Rescue Committee (IRC) said that incidents of rape near camps for those displaced by the fighting were becoming more common.
The IRC called on the AU to increase patrols, although these have been scaled down.
In Kalma - Darfur's biggest camp for internally displaced people - there used to be two to three reports of sexual violence a month, the IRC says.
But in the past five weeks, the figures has spiralled to 200 women and young girls, some as young as 13.
It is yet further evidence, relief workers say, that security is worsening in one of the most troubled regions of the world.
There has also been an escalation of attacks against humanitarian aid workers, some of whom have had to cease operations.
A peace deal was signed last May between the government of Sudan and a faction of the Sudan Liberation Army rebels, yet the bloodshed continues to force tens of thousands of people to seek refuge in camps.
Some two million people have fled their homes in the conflict, which began in February 2003, when Darfur rebels took up arms, accusing the government of ignoring the region.