A months-long standoff over the Dakota Access oil pipeline took a violent turn Thursday, when law enforcement officers used pepper spray and high-pitched warning tones to force protesters from a camp on private land in the pipeline’s path in North Dakota, and at least one demonstrator opened fire on police, authorities said.

Hundreds of local police officers and National Guard soldiers in riot gear began closing in on the protesters at midday, slowly advancing on the camp of about 200 with trucks and military Humvees, arresting people who refused to leave. By the end of the day, at least 141 protesters had been arrested, according to the Morton County Sheriff’s Office.

One protester fired three shots from a .38-caliber revolver as police tried to arrest her, nearly hitting a deputy, the sheriff’s office said, adding that the woman was taken into custody and no law enforcement officers returned fire. In a separate incident, a “private individual” near the protests was shot in the hand, police said. One man was arrested, but it was not clear whether he was a protester.

By evening, authorities said they had cleared the area and the remaining protesters had moved back down the road to an encampment on federal lands, where hundreds of people — from Native American tribes to celebrity environmental activists — have gathered since the summer to demonstrate against the pipeline.

Morton County Sheriff Kyle Kirchmeier said police would continue to guard the private land for the time being.

“We are not leaving the area,” he said. “We are holding it.”

The land, known as Cannonball Ranch, is in the path where Energy Transfer Partners plans to build part of the 1,172-mile pipeline. Protesters began camping there Sunday, setting up tents and teepees and barricading the nearby highway with tires, scrap wood and bales of hay.

One of the protest’s organizers, Dallas Goldtooth, said the demonstrators had braced for a show of force from authorities.

“This is not a loss, we always knew this camp was at risk,” he told the Bismarck Tribune. “We want the world to see how far North Dakota and their police will go to protect an oil company.”

The confrontation brought tensions between police and protesters to a new level. For months, authorities have allowed anti-pipeline activists to camp out on nearby land maintained by the Army Corps of Engineers. Some 260 people have been arrested in connection with the protests since mid-August — not counting those taken into custody Thursday — but the Army Corps has not evicted anyone so far, according to the Associated Press.

The $3.8 billion pipeline is slated to carry oil from North Dakota through the Midwest to an existing pipeline in Illinois, where it can be shipped to refineries elsewhere. Opponents of the project say it cuts too close to the Standing Rock Reservation and could pollute waterways and disrupt sacred land. The Standing Rock Sioux tribe has challenged the pipeline in court and accused authorities of violating their civil rights. Energy Transfer Partners says the pipeline offers a safer alternative to transporting oil than trucks, and North Dakota officials say the project would not harm cultural sites.

Before Thursday’s standoff, authorities asked protesters repeatedly to vacate the camp on Cannonball Ranch, saying they were blocking public roadways and occupying private property. Protesters refused to leave, contending that the land belonged to the tribe under an 1851 treaty, the Tribune reported.

On Thursday morning, police gave them a final warning, telling protesters over a megaphone that they would make no arrests if they returned to the main camp, according to the Tribune.

The scene grew chaotic when some protesters began throwing rocks and bottles at the lines of several hundred police officers and soldiers that had amassed around the camp. At that point, the Tribune reported, law enforcement officers wearing helmets and carrying batons began to inch toward the demonstrators, firing pepper spray, rubber bullets and smoke grenades, and blaring warning tones at the crowd.

As they retreated to a bridge on the highway, protesters set two fires and threw molotov cocktails at authorities, NBC reported. Photos from the scene show flames roaring out of piles of tires and thick black columns of smoke billowing into the sky.

Some protesters urged their counterparts to remain peaceful.

“Violence will be by them. We are here to protect the sacred, the water. Stand in prayer,” Mekasi Camp-Horinek, a protest organizer, told the Tribune. “We have the moral high ground.”

Law enforcement reported no serious injuries, but many protesters said their eyes were burned by pepper spray, while others said they were bruised by rubber bullets. One man was treated on the scene after hurting his leg, the AP reported.

Gov. Jack Dalrymple (R) praised authorities’ handling of the confrontation.

“Going forward, hopefully we have persuaded protesters that public roadways and private property is not the place to hold a protest,” he said.

Standing Rock Sioux Tribal Chairman Dave Archambault II criticized what he said was a “militarized” response from law enforcement.

“We won’t step down from this fight,” he said in a statement Thursday night. “As peoples of this earth, we all need water. This is about our water, our rights, and our dignity as human beings.”

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