U.N. Secretary General Ban Ki-moon failed, meanwhile, to persuade Egypt to push Sudan's leader to accept a U.N. peacekeeping mission in the region.
The convoy carrying humanitarian chief John Holmes was halted at a checkpoint about a mile outside the Kassab refugee camp, and he was told he lacked the proper papers for a visit there.
"I'm frustrated, annoyed, but it's not atypical of what happens here," Holmes told journalists traveling with him.
He said he had obtained all the necessary clearances from the government in Khartoum.
Other U.N. officials working in Darfur said that aid workers and U.N. staff were regularly blocked from doing their work at army checkpoints, and that Sudanese authorities had recently confiscated costly satellite gear from one convoy.
The soldiers at the checkpoint briefly prevented a car carrying journalists from leaving after Holmes turned back. The journalists were only allowed to leave after the troops confiscated a videotape from a U.N. television cameraman.
The Sudanese army spokesman, Sawarmy Khaled Taat, initially said he believed there had been a mix-up and that the U.N. had not obtained the proper permission for Holmes' visit.
But later Saturday, Sudanese authorities in El Fasher, capital of North Darfur, apologized, saying the incident was an individual mistake by Sudanese military intelligence personnel manning the checkpoint at Kassab, home to more than 25,000 refugees in a region under tight control of the janjaweed militia and government forces.
Holmes accepted the apology, the U.N. said.
Holmes, on his first trip to the region, said Friday he pressed Sudanese officials to grant better access to aid workers trying to help Darfurians amid widespread complaints that humanitarian groups face constant obstacles from the authorities in reaching victims of the conflict.
In need of aid are some 4 million people in Darfur caught in the midst of fighting between rebels, the government and the pro-government janjaweed. More than 200,000 people have been killed and more than 2 million displaced in four years of fighting, and the Arab janjaweed are accused of widespread atrocities against ethnic African civilians.
Ban, who is on a Mideast tour, said after an early morning meeting with President Hosni Mubarak that he had asked the Egyptian leader to exercise influence on Sudanese President Omar al-Bashir to accept the deployment of U.N. peacekeepers in Darfur.
Al-Bashir had earlier this month scuttled such a U.N. plan, rejecting its key points in a letter to Ban.
According to comments by Egyptian Foreign Minister Ahmed Aboul Gheit, Mubarak did not comply with the request to pressure his neighbor.
Aboul Gheit said that the way forward was through talks between al-Bashir's government and rebels who were not part of a peace agreement signed last year in Abuja, Nigeria, by the Sudanese government and one rebel group.