SOUTH OF BISMARCK, North Dakota (CNN) — The standoff over the Dakota Access Pipeline is heating up, and protesters say they won’t back down.
Long-brewing tensions over the controversial project boiled over Thursday, as police in riot gear faced off with protesters on horseback. After hours of clashes, law enforcement officials arrested 141 people.
A court decision allowing construction of the $3.7 billion pipeline across four states hasn’t dampened demonstrators’ furor over the project. The developer calls it an economic boon that will make the US less dependent on imported oil. But protesters say it threatens the environment and will destroy Native American burial sites, prayer sites and artifacts.
It’s unclear whether Thursday’s arrests will slow protest efforts at the construction site in Morton County, North Dakota.
But the message from law enforcement was clear as Humvees and helicopters flooded the area to break up an encampment near the pipeline’s path.
Police deployed bean bags, pepper spray gas and unleashed a high-pitched siren as they tried to disperse the crowd. Protesters lit debris on fire and threw Molotov cocktails, North Dakota Department of Emergency Services spokeswoman Cecily Fong said.
Authorities accused most of the arrested demonstrators of trespassing on private property. Supporters of the Standing Rock Sioux Tribe had earlier set up tents and teepees on the land, which they said belongs to the tribe under a 19th-century treaty.
By Thursday night, law enforcement had cleared the area and pushed protesters to the site of a previous encampment. Law enforcement lingered in vehicles from different agencies as trucks towed burned cars.
Both sides have accused the other of increasingly aggressive tactics, from police strip searches and violence, to protesters destroying construction equipment.
At least one person was injured Thursday, CNN affiliate KFYR reported. The extent of the injury was unclear.
Two people were arrested for allegedly firing gunshots Thursday; one near officers and another near a bridge north of the protester’s main camp.
“Most of these people are peaceful, prayerful people,” Fong said. “But we know that there is a faction that is willing to do anything to stop this pipeline. That’s why our people went down there prepared.”
One protester told KFYR that she felt helpless as police closed in.
“There are armed people standing there with their guns with their fingers on the trigger, and so I feel really helpless right now,” said Kandi Mossett of the Indigenous Environmental Network.
‘I’ve never been around so peaceful a stand’
The conflict has become a celebrity cause, drawing the support of the actress Shailene Woodley, who was arrested in an October 10 protest, and actor Mark Ruffalo, who provided infrastructure for the camp, including solar panels.
Ruffalo told CNN’s Jack Tapper that he did not witness violence when he visited there, but he heard stories from people who claimed they were thrown in jail naked.
Protesters are trained in peaceful resistance, he said. No one is allowed in the protest area without training.
“The mantra of the place is, ‘It’s not the police, it’s the pipeline that we’re protesting or protecting ourselves against.’ They spend basically the entire day doing prayers, chanting,” he said. “I’ve never been around so peaceful a stand.”
After the pipeline is completed, it would shuttle 470,000 barrels of crude oil a day, developer Energy Access Partners said. That’s enough to make 374.3 million gallons of gasoline per day. From Illinois, the oil could go to markets and refineries across the Midwest, East Coast and Gulf Coast.
Supporters say it would significantly decrease American reliance on foreign oil and free up railways to transport crops and other commodities.
The Standing Rock Sioux tribe and its supporters say pipeline construction will destroy burial sites, prayer sites and culturally significant artifacts. The tribe sued the US Army Corps of Engineers after it approved the project.
But an advocacy group says the tribe’s claims are misleading, saying the pipeline “does not cross into the Standing Rock Sioux Tribe’s reservation.”
CNN’s Euan McKirdy, Marlena Baldacci, Madison Park and Alberto Moya contributed to this report.