The UN secretary general is pressing Sudan's leader to accept non-African troops in the peacekeeping force due to arrive in Darfur within weeks.
The African Union force in Darfur is overstretched
In an interview with the Associated Press, Ban Ki-moon said he had dispatched two of his most senior envoys to a Lisbon summit.
In 25 days a joint African Union-UN force is due to deploy in Darfur but Khartoum insists that only African troops should be deployed.
Sudan's ambassador told the BBC the UN
was trying to excuse its own failings by blaming delays on his government.
Khartoum says it does not want contingents from Thailand, Nepal, Sweden and Norway in the 26,000-force due to take over from overstretched African Union troops in Darfur.
But the new mission has also been held back by its lack of 24 helicopters, vital for operating in a war-torn region the size of France.
Mr Ban is sending two senior UN officials to Lisbon, where Sudanese President Omar al-Bashir will be attending the European Union-Africa summit there this weekend.
The UN assistant Secretary General for Peacekeeping Operations, Edmond Mulet, and Mr Ban's deputy chief of staff, Kim Won-soo, are heading to Portugal on Thursday.
They will try to get the Sudanese leader to agree to the composition of the force and other issues, like giving permission for the peacekeepers to fly at night.
But Sudan's UN ambassador Abdalmahmood Abdalhaleem Mohamad said the peace force should ideally be drawn entirely from African countries.
"Whenever [the UN] have a failure, like to provide finance, failure to find helicopters... the shortest thing is to blame Sudan, say Sudan is dragging its feet," he told the BBC.
Some 200,000 people have been killed in Darfur since 2003
"I can assure you we are committed to deployment of the hybrid operation. We have accepted almost 97% of the composition of the force."
Mr Mohamad also dismissed calls by the prosecutor of the International Criminal Court for the arrest of two men accused of war crimes in Darfur.
ICC prosecutor Luis Moreno-Ocampo said he had strong evidence that the Sudanese Minister for Humanitarian Affairs Ahmad Harun and the leader of the pro-government Janjaweed militia, Ali Kuchayb, were involved in attacks on civilians in Darfur.
But Mr Mohamad said these claims were lies.
UN Security Council diplomats say the Sudanese do not want a credible force and that is why they are raising so many objections.
The secretary general has appealed to world leaders to help equip the peacekeepers but not a single helicopter has been pledged so far.
Countries are either overstretched or unwilling to send helicopters to Darfur.