The UN official responsible for humanitarian affairs, Jan Egeland, cut short a visit to Darfur on Friday after being denied access to certain areas of the war-torn region, a UN spokesman said.
"Egeland is currently in Khartoum after cutting his visit short," the spokesman said.
Sudanese authorities had refused to let Egeland access six areas in the centre and north of Darfur, citing security reasons, the spokesman added.
Egeland, who is on his last mission to Sudan as the United Nations humanitarian co-ordinator, had expected to spend three days in Darfur.
On Thursday he was barred by Sudanese authorities from entering camps for internally displaced people (IDPs) in Geneina, capital of West Darfur, also for "security reasons".
He met with representatives of the displaced at the UN Office for the Co-ordination of Humanitarian Affairs (OCHA) in Geneina and promised to highlight their plight.
"I will convey your message to the world," he told them.
According to the United Nations, 2.5 million people were displaced and at least 200,000 people were killed from the combined effects of fighting, famine and disease since ethnic minority rebels rose up in early 2003, drawing a scorched earth response from the government. Some sources say the toll is much higher.