The area affected by fire early Saturday was about 5,000 acres.

BISMARCK, N.D. (AP) — Containment of a large wildfire burning in the Little Missouri National Grassland of western North Dakota has reached nearly 90 percent.

The U.S. Forest Service says firefighters advanced containment by almost 20 percent Friday to early Saturday.

The area affected by fire early Saturday was about 5,000 acres.

The fire started a week ago in a remote area and isn't threatening any structures, people or livestock. The cause isn't known. Officials say the fire in some areas could continue to smolder for weeks.

About one-third of the Maah Daah Hey hiking, biking and horseback riding trail remains closed, along with two campgrounds.