Thousands of people had fled fighting between Sudan and South Sudan in the Heglig oil region even before renewed clashes this week, the United Nations said on Saturday.
About 10,000 people were displaced from villages around Heglig by recent clashes in the area, the UN's Weekly Humanitarian Bulletin said, citing the Sudanese Humanitarian Affairs Commission.
"They scattered to various locations, including Heglig town and other areas further north," the Bulletin said.
It covered the period to April 8 after initial clashes began in late March around the Heglig region, Sudan's most important oilfield, along the disputed border.
Last Tuesday even more intensive clashes began. The South reported aerial bombardment of its territory before its ground troops took over the Heglig region from Sudanese forces.
Sudan vowed to react with "all means" against a three-pronged attack it said was launched by the South.
The clashes, the worst since South Sudan won independence in July after one of Africa's longest civil wars, have brought the two former foes the closest yet to a return to outright war.
Heglig has been part of Sudan's South Kordofan state, where the government is also fighting ethnic minority rebels.
The United States and UN have called for aid access throughout the South Kordofan war zone to avert a humanitarian crisis. Sudan has cited security concerns in severely controlling access for foreign relief agencies.
Journalists are not allowed to report independently in the area.