About 300 opponents of the Dakota Access pipeline demonstrated in a North Dakota city on Thanksgiving Day, while protesters near the construction site where hundreds of demonstrators have camped out for months attempted to build a wooden bridge to reach what they say are tribal burial sites.

The protesters blocked traffic at an intersection and other streets in Mandan shouting "Shame on you, North Dakota!" and carrying a banner that read "No pilgrims, no pipeline," the Bismarck Tribune reported. About 50 officers stood across from the protesters, and the crowd eventually dispersed.

Morton County sheriff's office spokesman Rob Keller said officers near the campsites about 50 miles south of Mandan observed protesters attempting to build a wooden bridge over a body of water Thursday morning in an effort to reach Turtle Island, a hill where protesters claim burial sites are located. Keller said between 350 and 400 protesters eventually gathered at Turtle Island.

Keller said one protester told officers they were "ready to die today." Another said, "Remember '73?" referring to Wounded Knee.

In Portland, Oregon, hundreds of people rallied in the rain Thursday to show their solidarity with the Standing Rock Sioux Tribe and others who have spent months protesting the pipeline's construction.

The Oregonian/OregonLive reports (https://goo.gl/X4DGdy) that more than 350 people took part in the demonstration at the city's Pioneer Courthouse Square. Attendees chanted, "Stop the pipeline" and "Water rights are human rights."

Shannon Berger-Hammond co-founded a group called Families for Peaceful Protest, which organized the Portland rally. She said Thanksgiving is "meant to highlight peace and thanks and community and to celebrate indigenous nations, and the indigenous nations are suffering right now."

The Standing Rock Sioux and others oppose the 1,200-mile, four-state pipeline being built to carry oil from western North Dakota to a shipping point in Illinois because they say it threatens drinking water on the nearby reservation and cultural sites. Pipeline developer Energy Transfer Partners has said no sites have been disturbed and that the $3.8 billion pipeline will be safe.

The pipeline is largely complete except for the section under a Missouri River reservoir in southern North Dakota, and ETP Chief Executive Kelcy Warren has said the company is unwilling to reroute the project.

Protests against the pipeline have intensified in recent weeks, with arrests since August totaling more than 520.

Actress Shailene Woodley, who was among 27 activists arrested Oct. 10, was at one of the campsites Thursday. She live-streamed activities and was expected to help serve Thanksgiving dinner to protesters later in the day.

At least one person was arrested during Thursday's demonstration in Mandan, a community adjacent to the capital city of Bismarck. When protesters blocked the intersection, they set up several folding tables with pumpkins and a pig head. They also passed out food.

"They come at us with violence, we come back with prayer," Jamey Reil, of Virginia, said referring to a clash between police and protesters Sunday night near the campsites that sent at least 17 demonstrators to the hospital.

Law enforcement authorities in Burleigh County and Bismarck issued a phone alert Thursday morning warning residents about the presence of protesters. The recording urged people traveling to Burleigh and Morton counties during the Thanksgiving weekend to be on "alert to their surroundings."

Authorities also urged people to report any "suspicious activity." Authorities say "rioters" in the area intend "to create an unsafe environment for the public."