More than 2,000 US military veterans plan to form a human shield to protect protesters of a pipeline project near a Native American reservation in North Dakota, organisers said.
Veterans Stand for Standing Rock, the contingent led by former US Marine Michael A Wood Jr, will bolster thousands of demonstrators at camps located on US Army Corps of Engineers land, protest organisers said on a Facebook page on Wednesday.
US Representative Tulsi Gabbard, a Democrat from Hawaii and a major in the Hawaii Army National Guard, has said on Twitter she will join the protesters on Sunday.
Morton County Sheriff's Office spokesman Rob Keller said in an email his agency was aware of the veterans' plans, but would not comment further on how law enforcement officials would deal with demonstrators.
Meanwhile, North Dakota law enforcement will not make spot checks on vehicles headed to the camp where activists are based, the governor's office said on Wednesday, backing away from a previous plan.
Activists have spent months protesting plans to route the $3.8bn Dakota Access Pipeline beneath a lake near the Standing Rock Sioux reservation, saying it poses a threat to water resources and sacred Native-American sites.
The 1,885km pipeline project, owned by Texas-based Energy Transfer Partners LP, is mostly complete, except for a segment planned to run under Lake Oahe, a reservoir formed by a dam on the Missouri River.
"I figured this was more important than anything else I could be doing," Guy Dull Knife, 69, a Vietnam War veteran, told Reuters news agency at the main camp.
Dull Knife, a member of the Oglala Lakota tribe from the Pine Ridge Reservation of South Dakota, said he has been camping at the protest site for months.
The Army Corps, citing safety concerns, has ordered the evacuation of the primary protest camp by December 5, but said it would not forcibly remove people from the land.