BANGOR, Maine — The increasing tensions between law enforcement and Native Americans and others opposed to a proposed oil pipeline in North Dakota prompted a flash mob-style protest near the Bangor Mall on Friday that drew dozens of Maine tribal members and their allies.

The protest was highly visible as hundreds of shoppers headed to and from the mall and surrounding businesses in search of Black Friday bargains.

Penobscot Nation member Sherri Mitchell, an indigenous-rights lawyer, activist and educator and executive director of the Land Peace Foundation, said Friday that the standoff at Standing Rock is becoming increasingly violent.

Energy Transfer Partners’ $3.7 billion Dakota Access project has drawn steady opposition from environmentalists and Native American activists, led by the Standing Rock Sioux tribe, Reuters reported earlier this week.

Their tribal lands are adjacent to the Missouri River, where federal approval is needed to tunnel under a milelong stretch to complete the pipeline.

“They’ve been asked to stop [work on the pipeline] several times,” Mitchell said. “They don’t have a permit. They are refusing to stop. They are using more excessive force against the people there. That’s why we are gathering here today.”

The activist movement has grown steadily since the tribe established Sacred Stone Camp in Cannon Ball, North Dakota, in April, a temporary site founded as a point of resistance to the pipeline. The movement has remained strong even as temperatures have turned frigid.

The most violent clashes took place last weekend. Police used water hoses in below-freezing temperatures to keep about 400 protesters at bay, a move criticized by activist groups, the American Civil Liberties Union and elected officials concerned about freedom of expression and the escalation of violence.

Friday’s protest near the Bangor Mall was a peaceful one, drawing at least 150 tribal members and supporters from as far away as Portland.

Many of the tribal members turned out in their regalia and many brought drums. They and their supporters lined up along Bangor Mall Boulevard holding up large banners and smaller handmade signs calling for a stop to the pipeline.

During a flash mob in the intersection near Toys R Us at about 12:30 p.m., protesters drummed, sang and performed a traditional round dance — halting traffic for about five minutes.

Mitchell said that a woman named Sophia Wilanksy, whose father is a New York attorney, suffered serious injuries in an explosion earlier this week and may lose an arm.

Protesters alleged that the explosion was caused by a concussion grenade lobbed by police. National Public Radio reported that police claimed that the explosion was caused by protesters.

“There also was a number of people who had concussions,” Mitchell said. “Hundreds of people had hypothermia from being sprayed with water cannons in 40-degree temperatures for hours, so the injuries have been substantial and still nothing’s being done.

“The company has said they’re going to proceed with or without the permit. They’ll just pay the fine,” she said.

In addition, Penobscot Nation member June Sapiel said that her son, David Demo, a 25-year-old arborist from Deering, New Hampshire, was shot in the hand with a rubber bullet and faces reconstructive surgery in the week ahead.

“Unfortunately, it was his right hand,” she said, adding that it was not yet clear if her son will regain full use of his hand.

Demo was among dozens of protesters who were arrested late last month during a standoff between law enforcement and demonstrators seeking to halt construction of the disputed oil pipeline.

Mitchell and Sapiel are among a group of about a dozen people who are heading out to Standing Rock on Friday of next week. They said they are gathering medical supplies, warm blankets, winter coats, hats and gloves and other necessities for the protest, which had no end in sight as of Friday.

“We’re going to be sending people up for the winter and supporting them completely through the winter,” Mitchell said. “Every month we’re going to be cycling people out until it’s done.”

When the protest will end remains unknown, she said. She said it will go on for “as long as it takes. This is only the beginning because the stand for our water is going to be until we get them to switch from destructive practices to sustainable practices and so I don’t anticipate that this is going to end anytime soon.

“We’re in it for the long haul. Life depends on it,” she said.