The UN Security Council on Monday authorized a 4,200-strong temporary peacekeeping force to be deployed in Sudan's disputed Abyei region for six months.
Approval of the U.S.-sponsored resolution came amid worries about fighting in oil-rich Abyei as South Sudan prepares to declare independence from the north on July 9.
The United Nations has a 10,400-strong peacekeeping force monitoring implementation of the 2005 north-south agreement, but the Sudanese government informed the UN that it wants UN troops in the north to leave on July 9 when the south becomes independent.
As a result, the UN created a new mission for South Sudan.
U.S. Secretary of State Hillary Rodham Clinton said the decision to send in 4,200 Ethiopian peacekeepers is a "critical step" in implementing an agreement by the two sides to withdraw their forces from the Abyei region.
The north's Khartoum-based government and South Sudan's officials last week said they would demilitarize the contested border region near major oil fields.
Sudan welcomed the resolution as a "step forward."
Clinton said despite Monday's action, the United States remains concerned about the ongoing crisis in the region's Southern Kordofan area.
"Tens of thousands of people have been driven from their homes, and there are reports of very serious human rights abuses and violence targeting individuals based on their ethnicity and political affiliation," she said.
South Sudan's independence remains on schedule, but key issues remain unresolved including Abyei's future and demarcation of borders.