One person has been arrested after hundreds of protesters opposed to a North Dakota oil pipeline project clashed with police who fired tear gas and water cannons, officials said.
An estimated 400 protesters mounted the Backwater Bridge on Sunday and attempted to force their way past police in what the Morton County Sheriff's Department initially described as an "ongoing riot", the latest in a series of demonstrations against the Dakota Access Pipeline.
The sheriff's office said the protesters attempted to "attack" police barricades, demonstrating against the project they say threatens water resources and sacred tribal lands.
Demonstrators tried to start about a dozen fires as they attempted to outflank and "attack" law enforcement barricades, the sheriff's statement said.
Police said they responded by firing volleys of tear gas in a bid to prevent protesters from crossing the bridge.
The sheriff's department said officers on the scene of the latest confrontation were "describing protesters' actions as very aggressive".
Activists at the scene said on Twitter that police were also spraying protesters with water in sub-freezing temperatures and firing rubber bullets, injuring some in the crowd.
Police did not confirm the use of rubber bullets or water.
IN PICTURES: Dakota Access Pipeline protest
The Backwater Bridge has been closed since late October, when activists clashed with police in riot gear and set two trucks on fire, prompting authorities to forcibly shut down a protesters' encampment nearby.
The North Dakota Department of Transportation closed the Backwater Bridge due to damage from that incident.
Protests against the $3.7bn Dakota Access project has been mounted for months by the Standing Rock Sioux, whose reservation lies near the pipeline route, and the tribe's allies, who fear a leak could contaminate their drinking water.
They also worry that construction could threaten sacred sites.
Supporters of the pipeline, owned by Energy Transfer Partners, said the project offers the fast and most direct route for bringing Bakken shale oil from North Dakota to US Gulf Coast refineries and would be safer than transporting the oil by road or rail.
The company said no sites have been disturbed and that the pipeline will have safeguards against leaks.
READ MORE: Dakota pipeline - 'It's our right to live unharmed'
Completion of the pipeline, which will run 1,172 miles from North Dakota to Illinois, was delayed in September so federal authorities could re-examine permits required by the Army Corps of Engineers.
Plans called for the pipeline to pass under Lake Oahe, a federally owned water source, and to skirt the Standing Rock Sioux Reservation by about half a mile.
On Friday, Kelcy Warren, the chief executive of Dallas-based Energy Transfer Partners, said the company is unwilling to reroute the pipeline.
Source: News Agencies