Law enforcement officials used water cannons in below freezing weather to douse protesters as an ongoing demonstration near the site of the Dakota Access pipeline in North Dakota took an ugly turn.

The Morton County Sheriff’s Department say its deputies and other officers on the scene late Sunday were dealing with what the department termed an “ongoing riot.” The department said hundreds of protesters tried to get past a highway bridge that has been blocked for weeks, while also setting a number of fires.

“Protesters in mass amounts, estimated to be around 400, are on the bridge and attempting to breach the bridge to go north on Highway 1806,” the department said in statement late Sunday. “Protesters have started a dozen fires near the bridge.”

Protest group says hundreds hurt

But the protesters are telling a different story, with one of the groups involved in the demonstration saying hundreds of people were hurt when they were hit by water cannon blasts or rubber bullets. The protest group Camp of the Sacred Stones says demonstrators were trying to clear the blocked bridge so that emergency vehicles could get through in the event of an emergency, when law enforcement opened up with the water cannons and rubber bullets, as well as tossing tear gas into the crowd.

National Lawyers Guild legal observers on the front lines have confirmed that multiple people were unconscious and bleeding after being shot in the head with rubber bullets, the group said. “One elder went into cardiac arrest at the front lines but medics administered CPR and were able to resuscitate him.”

The group says the camp’s medical staff and its facilities were overwhelmed during the clash, but that a gym in nearby Cannonball had been opened up to accommodate injured and soaked protesters.

Bernie Sander calls on president to act

The incident Sunday prompted Vermont senator and former presidential hopeful #Bernie Sanders to call on President Obama to move to defend the protesters, who he says have gathered peacefully.

Protesters -- calling themselves “water protectors” -- have been camped out in the area for months as they try to stop construction of a #pipeline that would carry oil under a reservoir near the Standing Rock Sioux reservation. The tribe, its allies and others against the pipeline say the tribe’s water supply would be contaminated if there were a leak in the line. They also say the pipeline threatens sacred land.

The pipeline company -- Energy Transfer Partners -- says there are safeguards against the pipeline leaking and that it has gone through an extensive permitting process in order to complete the project. The Dallas-based company also argues that transporting oil through a pipeline is safer than shipping it by train or by truck.

Meanwhile, as protesters prepared to square off again with law enforcement officers on the scene Monday morning Energy Transfer Partners announced it was being purchased by Sunoco Logistics, in a deal worth nearly $20 billion. It’s not known what effect, if any, the purchase would have on the pipeline project. #Dakato access pipeline