Protesters sit in silence during a protest against plans to pass the Dakota Access pipeline near the Standing Rock Indian Reservation, near Cannon Ball, North Dakota, U.S., November 18, 2016.

Clashes between protesters and authorities over the Dakota Access Pipeline escalated Sunday night after an estimated 400 people tried to breach a law enforcement barrier, North Dakota law enforcement officials said.



The Morton County Sheriff's Office described the clash as a "riot" prompted by "very aggressive" activists, while protesters said authorities used tear gas, rubber bullets and water cannon in below-freezing temperatures.

NBC News couldn't independently confirm the use of rubber bullets, and a sheriff's spokesman, Rob Keller, told NBC News that no water cannon were deployed. He said the water was being sprayed from a fire truck to control blazes as they are being set by activists.

Atsa E'sha Hoferer of the Walker River Paiute Tribe, who called himself a "water protector," said he was hit with tear-gas and sprayed with water. Hoferer said demonstrators were lighting fires to provide warmth in the 25-degree weather.

More from NBC News:

What Will a Trump Presidency Mean for the Dakota Access Pipeline?

Scores Arrested in Dakota Access Pipeline Protests Nationwide

Army Corps of Engineers Says Pipeline Construction Can't Continue Without Tribe Input



"They're saying that we're causing multiple fires out here, but we're really only using them to stay warm," said Hoferer, 27. "I'm just a father with a phone that loves his water, that wants his water to be clean for his children and grandchildren."

In a statement, the sheriff's office acknowledged that tear gas and other "less than lethal means" were being used after protesters "engaged in organized tactical movement and attempted to flank and attack" a law enforcement line near a bridge.

The bridge had been closed since late October, when it was damaged in a fire after authorities evicted protesters from property owned by the pipeline developer.