Social media users are blasting security forces guarding the Dakota Access oil pipeline, after police used water cannons to repel protesters on a frigid night at the highly contentious site.

The Morton County Sheriff's Department says it deployed water cannons to quell an "ongoing riot" on a bridge near Cannon Ball, N.D., where approximately 400 activists were attempting to breach a police blockade to reach state Highway 1806. Police say the protesters had started several fires.

Security forces allegedly used rubber bullets, concussion grenades and tear gas in addition to the water cannons, causing a number of injuries, according to Dallas Goldtooth of the Indigenous Environmental Network. He said 17 individuals were sent to hospital to be treated for injuries and, in some cases, hypothermia.

The weather overnight was -2 Celsius, enough for the water to freeze in puddles around the protest site.

Police shared a photo of the protest overnight, while several anti-pipeline protesters shared images and videos of their own online.

The area has become the site of a long-running protest on behalf of the Standing Rock Sioux tribe, whose reservation lies close to the pipeline route in the southern part of North Dakota. The effort has captured international attention, including on social media, where the water cannon incident on Sunday night drew widespread outrage.

Among those voicing their distaste were the likes of Bernie Sanders, Al Gore, Mark Ruffalo and Alicia Keys.

Pipeline protester Kevin Gilbertt shared graphic images on Monday of a protester with a gruesome hole in her arm exposing the bone, which he says she sustained during the protest. "She was injured with either a concussion grenade or a non-lethal projectile," Gilbertt wrote.

He later removed the photos at the request of the woman's family.