Standing Rock Sioux Tribe urges calm as National Guard called in before pipeline ruling

The leader of the Standing Rock Sioux Tribe in North Dakota is urging calm ahead of a highly anticipated court ruling that could halt work on the contentious Dakota Access pipeline project.

Thousands have gathered in and around the reservation to support the tribe's fight against the pipeline, which many fear could leak and contaminate the Missouri River. The tribe was successful in getting a temporary work halt on portions of the pipeline earlier this week.

• Tribe 'disappointed' with judge's partial halt to North Dakota pipeline work 

But the temporary work stop came only after a violent confrontation over the weekend between people from the camp and private security guards armed with dogs and pepper spray.

Tribal chair David Archambault said that regardless of how the Federal Court rules on Friday, he doesn't want to see a repeat of that conflict.

"Any act of violence hurts our cause and is not welcome here," he said in a statement released on Thursday. 

"We invite all supporters to join us in prayer that, ultimately, the right decision — the moral decision — is made to protect our people, our sacred places, our land and our resources."

More police, National Guard

But also on Thursday, North Dakota Gov. Jack Dalrymple announced that the National Guard would be providing backup to police along highways leading to the reservation.

Armed guardsmen would replace state police and sheriffs who had been operating a traffic stop on Highway 1806, which links Bismarck with Standing Rock. 

"A small number of N.D. National Guard personnel will support law enforcement to augment public safety efforts," said a statement from the Morton County Sheriff's Department, a county that shares a border with the reservation.

A further 100 National Guard members will also be on standby.

National Guard won't enter camp

A camp set up to support the Standing Rock Sioux Tribe's fight against the oil pipeline has swelled over the past few days, now populated by thousands of people from across North America.

Few in that camp seemed concerned about the increase in police, though some reported already seeing unmarked vehicles with out-of-state licence plates in the area.

Archambault said he was told by the governor that National Guard would not enter the camp.