Citing public safety concerns, federal officials plan to close access to a campsite where demonstrators have protested the construction of a crude oil pipeline near the Standing Rock Sioux Reservation in North Dakota and create a “free speech zone.”

The Army Corps of Engineers, in a letter Friday to the chairman of the Standing Rock Sioux Tribe, Dave Archambault II, said the decision had been made to “protect the general public from the violent confrontations between protesters and law enforcement officials that have occurred in this area.”

Mr. Archambault said in a statement that the tribe was “deeply disappointed” by the decision.

“It is both unfortunate and disrespectful that this announcement comes the day after this country celebrates Thanksgiving — a historic exchange between Native Americans and the first immigrants from Europe,” he said. “Although the news is saddening, it is not all surprising given the last 500 years of mistreatment of our people.”

The authorities will close the area north of the Cannonball River, including the Oceti Sakowin camp, about 40 miles south of Bismarck, where opponents of the 1,170-mile Dakota Access Pipeline have gathered for months.