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Construction on the four-state Dakota Access pipeline resumed Tuesday on private land in North Dakota that's near a camp where thousands of protesters supporting tribal rights have gathered for months.

In turn, protesters said they're discussing nonviolent opposition measures, including chaining themselves to equipment. And at least eight people were arrested Tuesday attempting to shut down pipelines in other states as a show of solidarity with the Dakota Access protesters.

Texas-based Energy Transfer Partners resumed digging trenches and laying pipe, Morton County Sheriff's Office spokesman Rob Keller said, a move that comes in light of Sunday's federal appeals court ruling that allowed construction to resume within 20 miles of Lake Oahe. That Missouri River reservoir that is the water supply for the Standing Rock Sioux Tribe's reservation.

"We reiterate our commitment to protect cultural resources, the environment and public safety," the company said in a statement earlier Tuesday. The $3.8 million, 1,200-mile pipeline from North Dakota to Illinois is otherwise largely complete.

The work area is about 20 miles from the so-called Red Warrior Camp where scores of protesters have gathered in recent months.

Energy Transfer Partners still needs approval from the U.S. Army Corps of Engineers to work on a separate parcel of federal land bordering and under Lake Oahe, which the agency manages. The Corps said Monday it was not ready to give that approval because it is still reviewing whether reforms are needed in the way tribal views are considered for such projects.

The Standing Rock Sioux wants construction halted because of concerns about potential contamination of its water supply and says the pipeline will encroach on tribal burial sites and other cultural artifacts.

A state archaeologist's inspection found no such artifacts on the private land where construction will resume. The tribe disputes that, and is still appealing a lower-court ruling from September that allowed work on the entire pipeline to proceed.

Protesters will discuss nonviolent measures to oppose the resumption of construction, camp spokesman Cody Hall said Tuesday. Methods might include chaining themselves to equipment, as they have done in the past, but nothing had been decided early Tuesday, he said.

"The people are going to stay vigilant. They're going to fight this pipeline to the very end," he said.

In early September, tribal officials accused construction crews of bulldozing several sites of "significant cultural and historic value," leading to a clash between protesters and private security guards hired by the pipeline company. No one was arrested, and at least 30 people were pepper-sprayed.

Thousands of people have joined the protest in support of the tribe, and dozens have been arrested at construction sites, including actress Shailene Woodley and Green Party presidential candidate Jill Stein.

The eight who were arrested Tuesday in Minnesota, Montana, North Dakota and Washington state were targeting pipelines that move oil from Canada to the United States, according to Jay O'Hara, a spokesman for the environmental activism group Climate Disobedience Center.

"We are joining in support and in solidarity with those folks who are on the front lines in Cannonball, North Dakota," he said.

Pipeline company officials confirmed attempts in Minnesota and Montana, while the attempts in the other two states could not be immediately verified.

Officials with Spectra Energy's Express pipeline in Coal Banks Landing, Montana, say they received 20 minutes' warning from protesters and shut down the line. The pipeline had not been re-started as of late Tuesday morning and it was not immediately clear when it would begin flowing again, company spokesman Creighton Welch said.

A Kinder Morgan spokeswoman says they're "looking into things" regarding its Trans-Mountain pipeline in Anacortes, Washington.

And Enbridge spokeswoman Lorraine Little said protesters used bolt cutters to cut chains off a valve site on the company's pipeline in Leonard, Minnesota, leading the company to temporarily shut it down. She said it won't affect deliveries to customers.

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Associated Press writers Dave Kolpack in Fargo, North Dakota, Matt Volz in Helena, Montana, and Phuong Le in Seattle contributed to this report. Follow Blake Nicholson on Twitter at: http://twitter.com/NicholsonBlake