A federal judge declined to halt construction of part of the Dakota Access pipeline on Tuesday, despite pleas from the Standing Rock Sioux tribe that sensitive cultural artifacts are being destroyed. The decision could heighten tensions between the Native Americans protesting the project and the pipeline builder, a situation that’s become increasingly volatile.

The Standing Rock Sioux had filed an emergency motion for a temporary restraining order on Sunday, after pipeline builder Dakota Access LLC bulldozed a section of the route west of Lake Oahe, N.D., which contained sacred sites and historical artifacts. One of the sites was a stone marker that the Tribe’s cultural expert described in court filings as “one of the most significant archaeological finds in North Dakota in many years.”

Judge James Boasberg of the U.S. District Court for the District of Columbia did grant part of the restraining order, but only for a piece of the pipeline route east of Lake Oahe. That segment is not known to contain cultural artifacts.

David Archambault II, the tribe’s chairman, said in a statement that he was disappointed with the judge’s decision, which “puts my people’s sacred places at further risk of ruin and desecration.”

Dakota Access did not return requests for comment.

Opponents of the oil pipeline say they believe the company deliberately sought to destroy the artifacts, which are located along a two-mile stretch west of Lake Oahe. Dakota Access, a subsidiary of Dallas-based Energy Transfer Partners, began bulldozing that area on Saturday—less than 24 hours after the tribe filed a court document detailing the 27 graves, 16 stone rings, 19 effigies and other artifacts found there. By Sunday, all of those sites had been destroyed or harmed, according to court filings.

“It’s hard to say that it would be a coincidence,” said Stephanie Tsosie, one of several attorneys who filed the restraining order on behalf of the tribe. Tsosie works for Earthjustice, an environmental advocacy law firm based in Seattle.

Mekasi Camp Horinek, a member of the Ponca Nation of Oklahoma and coordinator of the advocacy group Bold Oklahoma, said there had been no recent construction along that part of the pipeline route until Labor Day weekend, when Dakota Access “leapfrogged about 10 miles from where they were to go to those culturally significant sites and destroy them.”

Patrick Parenteau, a law professor at Vermont Law School, said the timing “paints a very black picture” of the company’s behavior.

He said that under federal law, the discovery of Native American cultural artifacts should “stop the pipeline dead right there.” And if Dakota Access has bulldozed those sites, “that’s a crime.”

Parenteau said the U.S. attorney general or other federal agencies “should be sending in investigators. They should be on the scene.”

The construction led to a tense confrontation on Saturday. Dallas Goldtooth, a campaign organizer for the Indigenous Environmental Network, said a group of protesters—who call themselves “protectors”—were holding a prayer gathering near the site of the artifacts when they saw the bulldozers coming over the hill. The group then moved in to try and stop construction.

Protesters, as seen in a video by Democracy Now!, yelled as they climbed over a wire fence onto the construction site as a helicopter circled overhead. Private security guards with leashed dogs tried to disperse the crowd, which included children, and at one point an unleashed dog leaped at a group of protesters. The video shows a guard dog with blood on its nose and teeth. Near the end of the video, the security guards, who were outnumbered, got into their vehicles and drove away.

The Associated Press reported that four security guards and two dogs were injured during the confrontation. Goldtooth said at least 12 people, including a pregnant woman, were bitten by dogs, and the guards also used pepper spray.

The tribe has opposed the pipeline since it was rerouted last year to skirt the reservation’s land and cross the Missouri River upstream, which it believes threatens its water supply as well as the cultural sites in the pipeline’s path. The tribe filed a lawsuit in July alleging that the U.S. Army Corps of Engineers—the main federal agency involved in permitting the pipeline—failed to adequately assess the project’s environmental and cultural impacts.

When the Tribe requested a preliminary injunction to stop the construction beneath the Missouri River until the case can be tried in court, Boasberg delayed that decision, which is expected by Friday. 

The proposed 1,172-mile pipeline would move about half a million barrels of oil per day from North Dakota’s Bakken oil fields to Illinois.

The company rerouted the pipeline, originally slated to pass through Bismarck, closer to the Standing Rock Sioux reservation. Three federal agencies, including the Environmental Protection Agency, raised serious concerns about the environmental justice impacts, but the Army Corps dismissed them.

Resistance to the pipeline has grown for months, with hundreds of activists, mostly Native Americans, camping at a field near Cannon Ball, N.D.

The tribe’s lawsuit alleges the Army Corps gave the tribe little opportunity to conduct cultural surveys. Tim Mentz, Sr., the Standing Rock Sioux’s cultural expert, couldn’t survey the route near Lake Oahe until last week, when a local landowner invited him to take a look. By that point, more than half of the pipeline had already been built.

Mentz explained in court documents that he did not have permission to step onto the pipeline route. But many of the sites along the route were so prominent that he could identify them from a distance, and he also found important artifacts on the land adjacent to the route. Mentz’s survey identified five stone features “of very great cultural and historic significance,” all of which are now gone.