(Reuters) - North Dakota authorities are investigating a weekend incident in which pipeline protesters said a woman was struck by a man driving a truck who drove over her feet and fired shots into the air.

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The Morton County Sheriff’s Department is looking into what occurred, spokesman Rob Keller said in an email on Sunday, declining to comment further because the investigation is ongoing.

Early on Saturday, protesters against the oil pipeline near sacred tribal lands briefly blocked two entrances to a work yard near the rural town of Mandan, causing workers to leave the area.

Videos and pictures posted online show a man in a white vehicle holding a handgun and yelling obscenities while driving forward through a crowd of protesters. One video shows the man later raising his gun into the air and firing several shots, although it is not clear from the video whether any protesters were nearby at the time. The man was not identified.

A protester was injured in the incident and an ambulance was called, but she refused treatment, Keller said.

The circumstances of the injury were not clear, but one video shows the man striking a woman while she hangs off the truck’s side-view mirror. Protesters said on Facebook that a woman’s hand had been smashed, requiring three stitches on a finger, and that her feet had been run over. The woman could not immediately be reached for comment.

Vicki Granado, a spokeswoman for Dallas-based Energy Transfer Partners, the company leading the construction of the pipeline, said the man with the gun “is not associated with the pipeline project in any way.”

“It is my understanding he lives in the area and was just trying to get where he needed to go and felt threatened,” Granado said in an email.

Protests have sometimes turned violent over the $3.8 billion Dakota Access construction project, which has drawn steady opposition from Native American and environmental activists since the summer.

Last month, a demonstrator was charged with the attempted murder of a law enforcement officer. Authorities said she fired at a police officer three times during a struggle without hitting him.

The 1,172-mile (1,885-km) pipeline, being built by a group of companies led by Energy Transfer Partners LP ETP.N, would offer the fastest and most direct route to bring Bakken shale oil from North Dakota to U.S. Gulf Coast refineries.