BISMARCK, N.D. — A New York woman seriously hurt protesting the Dakota Access oil pipeline faces multiple surgeries and could lose an arm, her father said Tuesday, and protesters and law enforcement gave conflicting accounts about what might have caused the explosion that injured her.

Sophia Wilansky, a 21-year-old recent graduate of Williams College, was listed in serious condition and was undergoing surgery at a Minneapolis hospital.

Wilansky’s father, Wayne Wilansky, said his daughter was hurt when law enforcement threw a grenade. The Morton County Sheriff’s Office maintains authorities did not use concussion grenades or any devices that produce a flash or bang during a clash late Sunday and early Monday near the camp along the pipeline route in southern North Dakota where protesters have gathered for months.

The sheriff’s office suggested in a statement Monday that an explosion heard during the skirmish might have been caused by small propane tanks that authorities said protesters had rigged to explode.

Williams College held a small prayer service Tuesday night for Wilansky.

“The Williams community is deeply concerned about her,’’ Williams spokeswoman Mary Dettloff said in an e-mail. “She has many friends here and was very active in environmental activism as a student.’’

Dallas Goldtooth, a protest organizer with the Indigenous Environmental Network, did not immediately respond to a request for comment Tuesday. Wayne Wilansky disputed the claim by authorities, saying ‘‘there’s multiple witnesses and my daughter, who was completely conscious, said they threw a grenade right at her.’’

The North Dakota Highway Patrol backed the sheriff’s office’s version of events, saying officers during the skirmish spotted protesters with ‘‘multiple silver cylinder objects.’’

‘‘It was at this time an explosion occurred and several protesters ran to the area, pulled a female from under the burned vehicle, and fled the scene,’’ the patrol said.

Officers who investigated found 1-pound propane tanks ‘‘including one that appeared to be intentionally punctured,’’ the agency statement said.

During the clash, officers using tear gas, rubber bullets, and water sprays against protesters who they say assaulted officers with rocks, asphalt, water bottles, and burning logs. One officer was injured when struck in the head with a rock. At least 17 injured protesters were taken to hospitals.

Wayne Wilansky denounced the law enforcement tactics, saying ‘‘this is not Afghanistan, this is not Iraq. We don’t throw grenades at people.’’

Morton County Sheriff’s office spokeswoman Maxine Herr on Tuesday said authorities “continue to defend our tactics.’’

A GoFundMe account for Wilansky had raised more than $194,000 in 18 hours, with more than 7,200 people contributing. It was the highest trending account on Monday night, according to GoFundMe spokeswoman Kate Cichy.

The $3.8 billion pipeline to carry North Dakota oil to a shipping point in Illinois is largely complete outside of a stretch under a Missouri River reservoir in North Dakota near the Standing Rock Sioux Reservation. The tribe and others say the pipeline threatens the tribe’s drinking water along with American Indian cultural sites.

Travis Andersen of the Globe staff contributed to this report.