United Nations Secretary General Kofi Annan has warned Sudan that it will bear responsibility for any worsening of the humanitarian crisis in Darfur.
Some Sudanese are angry over the idea of UN peacekeepers
Mr Annan said Khartoum's resistance to a UN peacekeeping effort was putting at risk assistance for around 3m people.
Should aid agencies leave Darfur for lack of security, Mr Annan said, the Sudanese government would have to answer to the rest of the world.
A BBC correspondent says Mr Annan's language was unusually blunt.
His comments come as the African Union confirmed its decision to withdraw its peacekeeping troops from Darfur at the end of September.
The AU wants the UN to take over peacekeeping duties but Sudan strongly rejects this suggestion.
Fighting between pro-government militia groups and rebels demanding greater autonomy has left hundreds of thousands dead and many more homeless since 2003.
"The international community has been helping about 3 million people in camps and elsewhere and if we have to leave because of lack of security, lack of access to the people, then what happens?" Mr Annan said in the Egyptian town of Alexandria.
"The government [in Khartoum] will have to accept responsibility for doing this, and if it doesn't succeed, it will have lots of questions to answer to the rest of the world."
Sudan has been sending extra troops to Darfur ahead of the possible pull-out of the AU troops and violence there has intensified.
The International Rescue Committee aid agency says that one of its nurses was killed in fighting last Friday.
The 37-year-old Sudanese national was running a health centre in Hashaba, about 100km north of the North Darfur capital, el-Fasher.
The IRC says that 85,000 people in the area are now without health care.
The AU force has a weak mandate, is under-resourced, and numbers only 7,000 in an area the size of France.
AU deputy chairman Patrick Mazimhaka told the BBC that even if more money were forthcoming, political considerations made it difficult to stay longer.
The Security Council had hoped UN troops would replace AU troops
He was speaking after Sudan said the AU troops could remain if they accepted Arab League and Sudanese government funding.
A UN resolution passed last week, seeking to replace the AU force with 17,000 UN troops, was rejected by Khartoum.
The government has said it will replace the peacekeepers with its own force of 10,000 soldiers to the region, but the UN and rights groups operating in the region have expressed alarm at this idea.
The AU brokered a peace accord in May, but it was signed by the government and only one of the three main rebel groups in Darfur.
Since then, the violence has intensified.
Sudan's President Omar al-Bashir described the call for a UN force as "part of a comprehensive conspiracy for confiscating the country's sovereignty" in comments reported by the Sudanese news agency Suna on Sunday.
Darfur refugees, rebels and the United States have long accused the Sudanese army of backing up the Arab Janjaweed militias in a "genocide" against the region's black African population.
Sudan has denied these claims and says the problems in Darfur have been exaggerated for political reasons.
Last week, the UN's humanitarian chief Jan Egeland warned that "a man-made catastrophe of an unprecedented scale" loomed within weeks in Darfur unless the UN Security Council acted immediately.
But analysts say sending a UN force to the region without Khartoum's consent would be a virtually impossible task.