In North Dakota, tension over the 1,200-mile Dakota Access oil pipeline is escalating. Police and National Guard troops arrested more than 140 protesters near a construction site Thursday.

The Standing Rock Sioux have sued to stop the pipeline from crossing under the Missouri River next to their reservation, claiming the project would destroy sacred sites and threaten the water supply.

What started months ago as a dispute between a tribe and the federal government has escalated into clashes between protesters and police.

Hundreds of law enforcement in riot gear formed a line Thursday across the prairie and moved in on an encampment of tents and teepees. The protest camp was set up over the weekend along the pipeline route on land owned by the Dakota Access pipeline company. Officers were backed up by dozens of police cars, armored vehicles and aircraft.

Surveillance helicopters circled above a makeshift roadblock of beat-up cars, tires and wooden pallets. Protesters lit it on fire, trying to keep police out.

But police pushed protesters back, trying to get them to move farther down the highway.

"We won't have it anymore. This is our stand. We'll stand. And we'll stop this pipeline," said Robert Eder, a resident of Cannon Ball, N.D., the first town downstream from the pipeline's proposed river crossing. He was joined by hundreds of Native Americans from tribes across the country and by activists camped nearby since August.

The project is slated to carry crude oil from North Dakota's Bakken oil fields to Illinois. Pipeline supporters and state officials have given assurances it's safer than transporting crude by the trains that carry it across the very same river every day.

Protesters knew when they moved to private land owned by pipeline company Energy Transfer Partners last weekend that it would provoke a confrontation. And that came Thursday, with law enforcement barking orders over a speaker. Highway Patrol Lt. Tom Iverson says he was hoping not arrest anyone.

"If we could have come out here today and not made any arrests that would have been great," Iverson said. "But they forced us into arresting them."

Demonstrators remain adamant that the pipeline not cross under the water. And they unite in prayers, as well as with chants of "Black Snake Killaz." That's how some describe their purpose here: to kill the pipeline they have dubbed the black snake.

Jeff Chavis of South Carolina's Pee Dee Tribe says they won't back down until they stop the pipeline.

"They get their pipes. They get their machines. They get their people and they leave," Chavis said. "There's no negotiation."

On Thursday, the Republican governors of Iowa and the Dakotas urged the Army Corps of Engineers to issue the easement for construction to continue. This river crossing has been on hold since the federal government decided to review the permit. The Standing Rock Sioux Tribe has argued in court that the Corps failed to adequately consult it.

If construction is approved, the tribe says it will do everything it can to block it.

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