BISMARCK, N.D. – An elementary school went on lockdown Wednesday as authorities temporarily blocked the main road into St. Anthony to prevent Dakota Access Pipeline protesters from passing through the small town to get to pipeline construction sites.

An estimated 100 to 150 pipeline opponents ended up staging a protest on County Road 136 where law enforcement vehicles and armed officers blocked their caravan of about 80 vehicles and two buses, Morton County spokeswoman Donnell Preskey said.

“We’re concerned, with that many vehicles driving through town, it would interfere with the public safety of the school and the community. It would be hard for emergency vehicles to get through,” Preskey said, explaining the reason for the roadblock.

Protesters were advised to take other routes, Preskey said, though she added she heard law enforcement also was blocking some other nearby roads leading to construction sites for the $3.8 billion, 1,172-mile crude oil pipeline from the Bakken oilfields to Patoka, Ill. Protesters later moved to other sites in the area, and no arrests had been made as of 3 p.m., authorities said.

A woman who answered the phone at Little Heart Elementary School in St. Anthony confirmed the school was on lockdown but declined to comment further. Local residents also were notified of the roadblock, Preskey said.

Dakota Access temporarily stopped work at five different sites, Preskey said. A Dakota Access spokeswoman did not return messages seeking comment.

Joye Braun, an organizer with the Indigenous Environmental Network, said in a video taken at the roadblock and posted on the group’s Facebook page that Morton County was interfering with pipeline opponents’ rights to exercise free speech and peacefully assemble.

“We do have a right to go and be on public access where these workers are going. All we were doing was going to go drive, say some prayers, and … we were going to leave. Instead, the police escalated things, which is really sad,” Braun said in the video.

The sheriff’s department cited a section of state law that lists the sheriff’s duties, including that the sheriff shall preserve the peace and “prevent and suppress all affrays, breaches of the peace, riots, and insurrections which may come to the sheriff's knowledge.”

Preskey noted the work was taking place outside of a temporary no-construction zone that extends 20 miles east and west of the Missouri River at Lake Oahe, as ordered by a federal appeals court considering the Standing Rock Sioux Tribe’s request for an injunction to halt the pipeline. A three-judge appeals court panel in Washington, D.C., heard arguments Wednesday but did not rule on the injunction request, which a district court judge denied last month.

Authorities have arrested 96 people in connection with the protests since they began in mid-August.

Jon Eagle Sr., a tribal historic preservation officer for the Standing Rock Sioux Tribe, will be allowed to survey an area of the pipeline corridor that hasn't been disturbed by construction, Preskey said.

Eagle said he requested Morton County work with him for permission to survey an area of undisturbed land between state highways 1806 and 6. Eagle said he is "confident" the area has religious and cultural sites that can be protected if they're identified.

“If we work together we can identify and preserve these important things," Eagle said. "It’s part of our collective history. Once it’s gone, it’s gone forever.”

The tribe is disputing a report by state archaeologists who found that earthwork on a segment of the pipeline route Sept. 3 did not destroy sacred sites, after Dakota Access refused to allow tribal participation in that survey.

The North Dakota portion of the four-state pipeline was about 68 percent complete at the end of August, according to the most recent construction report filed with the state Public Service Commission.

Commission chairwoman Julie Fedorchak said the U.S. Pipeline and Hazardous Materials Administration gave the PSC an update Tuesday on its ongoing inspections of the pipeline welds, coatings and other aspects of construction.

Fedorchak said PHMSA “didn’t raise any concerns,” and it reinforced for her that modern pipelines are the preferred method of transporting crude oil, being safer than rail or trucks.

“We need to be careful in our regulatory processes that we aren’t discouraging that,” she said.

The Morton County Sheriff’s Department set a press conference for 1:30 p.m. Thursday at the county courthouse in Mandan to discuss changes in law enforcement’s stance toward the protests and the department’s unified command structure. Preskey said she couldn’t release additional details.

The North Dakota National Guard has been assisting state and local authorities in a limited capacity, with a handful of soldiers manning a traffic information checkpoint on Highway 1806 between Mandan and the protest camps in southern Morton County, about 25 miles southeast of St. Anthony. An additional 100 Guardsmen have been on standby alert.