The US Army Corps of Engineers said those protesting a North Dakota pipeline will not be forcibly removed.

US authorities have said there are no plans to forcibly remove activists protesting plans to run an oil pipeline under a lake near the Standing Rock Sioux reservation in North Dakota, despite telling them to leave by early December.

The US Army Corps of Engineers, which manages the government land where the main camp protesting the Dakota Access pipeline is located, said last week it would close public access to the area north of the Cannonball River on December 5.

On Sunday, the agency said in a statement that it had “no plans for forcible removal” of protesters. The statement said anyone who remained would be considered unauthorised and could be subject to various citations.

North Dakota pipeline protesters told to leave

It also said emergency services might not be adequately provided to the area.

“The Army Corps of Engineers is seeking a peaceful and orderly transition to a safer location,” the statement said. “This will reduce the risk of harm to people in the encampments caused [by] the harsh North Dakota winter conditions.”

A representative for the agency could not be immediately reached on Sunday to provide further clarification on its plans.

Organisers told a news conference on Saturday at the main protest site where about 5,000 people are camped that they had no intention of moving.

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There are smaller camps on land not subject to the planned restrictions, including an area south of the Cannonball River where the Corps said it was establishing a free-speech zone.

Demonstrators have protested for months against the $3.8bn Dakota Access Pipeline, owned by Energy Transfer Partners LP, saying it poses a threat to water resources and sacred Native American sites.

The companies say the pipeline would carry Bakken shale oil cheaply and safely from North Dakota to Illinois, en route to US Gulf Coast refineries.

The 1,885km project is mostly complete, except for the segment planned to run under Lake Oahe, less than 1 km north of Standing Rock.

The Obama administration, in September, postponed final approval of a permit required to allow tunneling beneath the lake, a move intended to give federal officials more time to consult tribal leaders. The delay also led to escalating tensions over the project.

Last weekend, police used water hoses in subfreezing weather in an attempt to disperse about 400 activists near the proposed tunnel excavation site.