UNITED NATIONS — The United Nations Security Council on Thursday approved a major reduction of peacekeepers in Darfur, the vast region of Sudan where violence continues against civilians, according to human rights groups, and millions remain displaced after years of fighting.

More than a third of the nearly 19,000 troops and police officers deployed in Darfur will start to be withdrawn, according to a resolution unanimously adopted by the Security Council. The resolution is part of a larger effort, led by the Trump administration, to reduce the United Nations peacekeeping budget.

The General Assembly is expected to vote on the new peacekeeping budget on Friday.

Violence has subsided in parts of Darfur, according to the United Nations secretary general, though human rights groups warn of the risk of heightened abuses against civilians after peacekeepers withdraw, and humanitarian aid agencies say that without peacekeepers nearby it will be difficult to deliver assistance. Nearly three million people remain displaced from their homes.

“While it’s hard to predict the immediate effect these cuts would have on civilian protection,” Omer Ismail of the Enough Project, a Washington-based advocacy group, said in an email, “we know the risk of conflict is high in many of the areas where bases are to be closed and military contingents are to be withdrawn.”