The report said on Sunday villages south of Zam Zam, 17km south of North Darfur's capital al-Fashir, had been attacked, but a UN official said it was not clear yet who was behind them.
The UN says the world's worst humanitarian disaster has been caused by fighting in the Darfur region that has displaced more than a million people and killed up to 50,000.
Sudan's government has come under mounting international pressure to end the conflict and disarm militias, or so-called Janjawid, which have been blamed for much of the violence.
"Attacks on villages south of Zam Zam have resulted in a population movement of around 3000 to 4000 persons," said the UN report, adding that half of those who had fled their homes had been moved to a camp in Zam Zam.
"There has been a sharp upturn in the number of attacks throughout the southern part of North Darfur," it said.
Rebels took up arms against the government in February 2003 after years of low-level clashes between nomads and farmers over scarce resources.
The rebels accuse the government of arming militias to loot and burn villages, a charge Khartoum denies. It says the Janjawid are outlaws.
Peace talks brokered by the African Union (AU) in the Nigerian capital Abuja have been dogged by accusations from both sides of ceasefire violations.
Rebels have been fighting the
government since February 2003
Rebel and government representatives were tight-lipped on Sunday on the state of the negotiations, but both sides were due to meet AU negotiators to discuss proposed amendments to a draft security document mooted by the African body.
Rebels said only the government and Janjawid could be responsible for the attacks near Zam Zam because it was too close to government-controlled al-Fashir.
"It must have been government forces or the Janjawid. No rebel group can go there because it is too close to the city,"
said Abd al-Hafiz Musa Mustapha, a spokesman for the Sudan
Liberation Movement rebel group.
Mustapha said fresh attacks had taken place on Sunday near the town of Jabalmoon, some 75km north of the West Darfur provincial capital Geneina, but no reports of casualties were immediately available.
Sudan government delegates at the talks declined to comment. The US said on Friday it was preparing a new UN resolution on Darfur and that US Secretary of State Colin Powell might soon address whether the violence in western Sudan constituted genocide.
The US Congress has already labelled the conflict genocide, but President George Bush's administration has not yet taken that step. Sudan denies carrying out genocide.