(CNN) Protesters have tried to stop the construction of the Dakota Access Pipeline since late last summer. They've voiced environmental concerns. They've performed sacred rituals. They've stood in solidarity with a Native American group seeking to be heard.

On Sunday night, 400 protesters clashed with police, leading to the hospitalization of more than two dozen.

One protester, a 21-year-old New York resident named Sophia Wilansky, nearly lost her arm after an explosion. How did it happen? Both sides have blamed each since the weekend clashes.

Billion-dollar brouhaha

The proposed Dakota Access Pipeline, which is set to cost $3.7 billion, would start in North Dakota, stretch across parts of South Dakota and Iowa and end in southern Illinois. If completed, the pipeline would allow crude oil to be transported to oil refineries along the Eastern Seaboard.

Wilansky was among the protesters Sunday who rallied in solidarity with the Standing Rock Sioux Tribe. Members of the tribe, whose reservation is near the project's path, believe the pipeline would affect its supply of drinking water and place downstream communities at risk of contamination from potential oil spills. The US Army Corps of Engineers granted the project final permits in July -- to the dismay of environmentalists and tribe members.

Michael Knudsen, medical logistics coordinator for the Standing Rock Medic and Healer Council, told CNN that demonstrators on Sunday had attempted to pull a truck off of the Backwater Bridge to clear a roadblock that "prevented people from being evacuated in an emergency."

Knudsen said he saw police unleash water cannons on protesters even though temperatures were below freezing. They also shot rubber bullets and tear gas toward the crowd.

"It was horrific," one protester told CNN. "It was a horrific scene."

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Frightening explosion, fears of amputation

As the protest stretched into Monday morning, police started to fire concussion grenades at protesters, Knudsen said.

Wilansky had been handing out bottles of water to protesters when a grenade landed near her forearm. Suddenly, it detonated, according to witnesses.

"She was air lifted to County Medical Center in Minneapolis were she's currently undergoing extensive, hours-long surgery from injuries sustained from the blast," said a GoFundMe page raising money for her medical costs.

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Initially, protesters feared the worst: Doctors would have to amputate her arm due to the explosion.

But Wayne Wilansky, Sophia's father, told CNN affiliate KFYR that amputation wouldn't be necessary even though the explosion "blew the bone out of her arm."

Wilansky noted his daughter, who might need as many as 20 surgeries to repair her forearm, still remained focused on the pipeline fight.

"Even though she's lying there with her arm pretty much blown off, she's focused on the fact that it's not about her, it's about what we're doing to our country, what we're doing to our native peoples, what we're doing to our environment," Wayne Wilansky said.

Police: We didn't fire grenades at protesters

On Tuesday, North Dakota State Patrol spokesman Lt. Tom Iverson told CNN affiliate KFYR that state troopers had not deployed a grenade or any other explosive against protesters on Sunday.

"There is no merit to that," Iverson said."But I assure the citizens of North Dakota ... that law enforcement is investigating this. All the facts will be out there."

The North Dakota Joint Information Center also released photos of improvised weapons that law enforcement said protesters used against them during the confrontation at Backwater Bridge.

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Authorities said they recovered a punctured propane cylinder, rocks and glass jars, which they said are commonly used to make Molotov cocktails.

According to KFYR, police say protesters were seen running to the area where the explosion had happened. The group pulled a female from under a burned vehicle on the bridge, then fled, authorities said.

'There are many witnesses'

However, Wayne Wilansky questioned Iverson's contention that police refrained from using grenades.

"There are many witnesses," Wilansky said. "They have scrap metal, and the sheriff's office says they did it to themselves -- that they blew up their own bombs or something. That's ridiculous."

Photos: North Dakota pipeline protests Photos: North Dakota pipeline protests Fireworks lit the sky at the Oceti Sakowin Camp near Cannon Ball, North Dakota on December 4, 2016, after the Army Corps of Engineers halted the Dakota Access Pipeline route. An executive order by President Donald Trump in January allowed work to resume. Hide Caption 1 of 32 Photos: North Dakota pipeline protests Activists embrace after the December halt of the Dakota Access Pipeline route. The $3.7 billion project that would cross four states and change the landscape of the US crude oil supply. The Standing Rock Sioux tribe says the pipeline would affect its drinking-water supply and destroy its sacred sites. Hide Caption 2 of 32 Photos: North Dakota pipeline protests An activist rides down from a ridge on the edge of the Standing Rock Sioux Reservation on December 4. Hide Caption 3 of 32 Photos: North Dakota pipeline protests Activists celebrate at Oceti Sakowin Camp on December 4. An executive order by President Donald Trump in January allows work to resume on the Dakota Access Pipeline, which the activists oppose. Hide Caption 4 of 32 Photos: North Dakota pipeline protests Dan Nanamkin of the Colville Nez Perce tribe drums a traditional song by the Cannonball River in Cannon Ball, North Dakota, on Thursday, December 1. Hide Caption 5 of 32 Photos: North Dakota pipeline protests A procession makes its way down to the Cannonball River to take part in a Native American water ceremony on December 1. Hide Caption 6 of 32 Photos: North Dakota pipeline protests Snow covers the camp on Wednesday, November 30. Hide Caption 7 of 32 Photos: North Dakota pipeline protests A person walks through snow and wind on Tuesday, November 29. Hide Caption 8 of 32 Photos: North Dakota pipeline protests People against the construction of the Dakota Access Pipeline speak at a news conference near Cannon Ball on Saturday, November 26. Hide Caption 9 of 32 Photos: North Dakota pipeline protests A sculpture stands at an encampment where protesters of the pipeline have been gathered for months. Hide Caption 10 of 32 Photos: North Dakota pipeline protests People protest along Highway 1806 as they walk past a sprawling encampment on Thursday, November 24. Hide Caption 11 of 32 Photos: North Dakota pipeline protests A man stands along Highway 1806 on November 24. Hide Caption 12 of 32 Photos: North Dakota pipeline protests In this image provided by the Morton County Sheriff's Department, law enforcement and protesters clash near the pipeline site on Sunday, November 20. Hide Caption 13 of 32 Photos: North Dakota pipeline protests Tonya Stands recovers after being pepper-sprayed by police on Wednesday, November 2. Stands was pepper-sprayed after swimming across a creek with other protesters hoping to build a new camp to block construction of the Dakota Access Pipeline. Hide Caption 14 of 32 Photos: North Dakota pipeline protests Dozens of protesters wade in cold creek waters as they confront local police on November 2. Hide Caption 15 of 32 Photos: North Dakota pipeline protests Tribe members make their way back to their camp on Saturday, October 29. Hide Caption 16 of 32 Photos: North Dakota pipeline protests Cousins Jessica and Michelle Decoteau take part in a protest outside the North Dakota state capitol in Bismarck on October 29. Hide Caption 17 of 32 Photos: North Dakota pipeline protests The burned hulks of heavy trucks sit on Highway 1806 on Friday, October 28, near a spot where Dakota Access Pipeline protesters were evicted a day earlier. Hide Caption 18 of 32 Photos: North Dakota pipeline protests Pipeline protesters sit in a prayer circle as a line of law enforcement officers make their way across the camp to relocate the protesters a few miles south on Thursday, October 27. Protesters had camped on private property. Hide Caption 19 of 32 Photos: North Dakota pipeline protests A protester is arrested as law enforcement surrounds the camp on October 27. Hide Caption 20 of 32 Photos: North Dakota pipeline protests Tires burn as armed soldiers and law enforcement officers stand in formation to force Dakota Access Pipeline protesters off the private land in Morton County. Hide Caption 21 of 32 Photos: North Dakota pipeline protests A protester shows where he was hit by a bean-bag round fired by officers trying to force protesters off the private land. Hide Caption 22 of 32 Photos: North Dakota pipeline protests JR American Horse leads a march to the pipeline site on Friday, September 9. Hide Caption 23 of 32 Photos: North Dakota pipeline protests Native Americans head to a rally at the state capitol in Denver on Thursday, September 8. They were showing their support for members of the Standing Rock Sioux tribe in North Dakota opposting the Dakota Access Pipeline. Hide Caption 24 of 32 Photos: North Dakota pipeline protests People hang a sign near what they say was sacred burial ground disturbed by bulldozers in Cannon Ball. Hide Caption 25 of 32 Photos: North Dakota pipeline protests Marlo Langdeau of the Lower Brule Sioux Tribe joins hundreds of Native Americans for a march near Cannon Ball on Sunday, September 4. Hide Caption 26 of 32 Photos: North Dakota pipeline protests Protesters march on September 4 in opposition to the Dakota Access Pipeline. Hide Caption 27 of 32 Photos: North Dakota pipeline protests Native Americans march to the site of a sacred burial ground on September 4. Hide Caption 28 of 32 Photos: North Dakota pipeline protests Native Americans ride with raised fists to the sacred burial ground on September 4 to protest the Dakota Access Pipeline. Hide Caption 29 of 32 Photos: North Dakota pipeline protests The Missouri River is seen beyond an encampment near Cannon Ball, where hundreds of people gathered to join the protest on September 4. Hide Caption 30 of 32 Photos: North Dakota pipeline protests Flags of Native American tribes from across the United States and Canada line the entrance to a protest encampment on Saturday, September 3. Hide Caption 31 of 32 Photos: North Dakota pipeline protests Phil Little Thunder Sr. attends an evening gathering at an encampment of Dakota Access Pipeline protesters on September 3. Hide Caption 32 of 32

Despite the gruesome injury to Sophia Wilansky, protesters vowed to move ahead with further protests.

As for the pipeline, construction has stalled as the Corps of Engineers engages in talks with Native American leaders.