A 21-year-old woman protesting construction of the Dakota Access oil pipeline in North Dakota last weekend was hospitalized in Minneapolis Tuesday after allegedly being struck by a grenade fired by a law enforcement officer, her father said.

Sophia Wilansky, of New York City, underwent surgery at Hennepin County Medical Center after her left arm was “pretty much blown off” by the grenade during the protest Sunday, her father, Wayne Wilansky, said at a news conference Tuesday.

A doctor has told the family that Wilansky will probably face many surgeries — up to 20 — to save her arm and hand, Wayne Wilansky said.

The Morton County Sheriff’s Office maintains authorities did not use concussion grenades or any similar devices in dealing with protesters Sunday.

It suggested in a statement Monday that an explosion heard during the skirmish between protesters and police might have been caused by small propane tanks that, authorities said, protesters rigged to explode.

However, Wayne Wilansky said several witnesses saw officers throw a grenade at his daughter.

Sophia Wilansky, a recent graduate of Williams College in Massachusetts, had joined the pipeline demonstration three weeks ago, her father said.

She was one of at least 17 protesters hospitalized after demonstrators tried to push past a long-blocked bridge on a state highway Sunday and were turned back by authorities using tear gas, rubber-coated bullets and water hoses, according to wire reports. She was airlifted to Minneapolis after the confrontation, her father said.

Christine Hill, a spokeswoman at HCMC, said Tuesday that Wilansky was in serious condition.

Wayne Wilansky said his daughter told him authorities fired a grenade directly at her forearm. He said she had been hit by 14 rubber-coated bullets before the grenade struck. He accused authorities of purposely hurting protesters to discourage others from joining the demonstrations, which have continued for months.

Demonstrators are supporting leaders of the Standing Rock Sioux tribe, which opposes the 1,200-mile, four-state pipeline that is being built to carry oil from western North Dakota to a shipping point in Illinois.

They contend the pipeline will threaten the reservation’s drinking water and disturb cultural sites.

Energy Transfer Partners, the pipeline builder, has maintained that the water supply is not in danger. It also has said that no cultural sites have been disturbed.

Clyde Bellecourt of Minneapolis, a founder of the American Indian Movement, which has supported the pipeline protests, coordinated Tuesday’s news conference, held on a sidewalk outside the Hennepin County Medical Center.

“We stand in total solidarity with Sophia Wilansky,” he said.

About 125 people supporting her attended a vigil outside the hospital late Tuesday afternoon.

The Associated Press contributed to this report.

Twitter: @randyfurst