BISMARCK, N.D. (AP) — A New York City woman who suffered a serious arm injury while protesting the Dakota Access pipeline last year is preparing for her fifth surgery, even as she faces assertions by the government that she or her fellow protesters are at fault for an explosion they blame on police.

Recently unsealed court documents indicate the government last spring sought evidence that might implicate Sophia Wilansky of federal crimes dealing with homemade explosives by searching her Facebook account.

Wilansky was injured during a violent clash between protesters and police in November 2016 that's become the emblematic skirmish of the months-long protest in North Dakota against the recently finished pipeline that's carrying oil to Illinois.

Protesters tried to push past a blocked highway bridge near their main encampment but were turned back by authorities using tear gas, rubber bullets and water sprays. Police said protesters threw objects including rocks, asphalt and water bottles at officers.

Wilansky suffered a left arm injury in an explosion. Protesters allege the blast was caused by a concussion grenade thrown by officers, while police maintain it was caused by a propane canister that protesters rigged to explode.

"There is probable cause to believe that violations (of explosives laws) have been committed by Sophia Wilansky," FBI Special Agent Brian VanOosbree said in an affidavit accompanying the March 28 application for a search warrant for her Facebook account.

Eight months later, Wilansky hasn't been charged with any crimes, though the investigation is ongoing, according to the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives. Both agencies declined to comment. Assistant U.S. Attorney Gary Delorme didn't respond to requests for comment.

Delorme received permission from a federal magistrate judge in March to keep the Facebook search secret. It was unsealed in late October. The FBI sought information that took 1 ½ pages to detail, from photos and videos to lists of friends.

"It did seem like one of the motivations of going after her Facebook account was to see her associates, to see her friends," said Wilansky's attorney Lauren Regan, who heads the Civil Liberties Defense Center.

Wayne Wilansky said he and his daughter weren't aware of the search but aren't surprised or worried by it.

"There's nothing on her Facebook page that would concern me," he said.

The family is planning to sue the FBI to obtain shrapnel that authorities took as evidence, hoping it will bolster an eventual lawsuit they plan to file against law enforcement seeking monetary damages.

Sophia Wilansky has limited use of her left arm and hand, which her father said is "totally disfigured." She's scheduled for tendon replacement surgery on Dec. 12.

___

Associated Press writer Amy Forliti in Minneapolis contributed.

___

Follow Blake Nicholson on Twitter at https://twitter.com/NicholsonBlake and Amy Forliti at https://twitter.com/amyforliti