The 1,172-mile (1,885-km) pipeline, being built by a group of companies led by Energy Transfer Partners LP, would offer the fastest and most direct route to bring Bakken shale oil from North Dakota to U.S. Gulf Coast refineries.

The project has faced months of protest from the tribe, as well as environmental activists, who say it threatens local water supplies and sacred tribal sites.

Supporters say the pipeline would be safer and more cost-effective than transporting the oil by road or rail.

Last week, protesters and law enforcement clashed as police swept demonstrators from a separate camp on private property and more than 140 protesters were arrested.

On Monday, a protester was charged with attempted murder of a law enforcement officer after authorities said she shot at police during the incident.

Archambault said the companies building the pipeline had “backed the tribe into a corner,” but he condemned the shooting incident.

“The tribe has maintained that this be a peaceful and prayerful demonstration,” he said.

Law enforcement agencies from eight states, including South Dakota, Minnesota and Ohio, have assisted the Morton County Sheriff’s Department in handling the protesters, according to a department spokeswoman.

On Tuesday, North Dakota’s Emergency Commission approved an additional $4 million loan to support law enforcement at the pipeline.

(Reporting by Timothy Mclaughlin in Chicago; Editing by Sharon Bernstein and Peter Cooney)