Law enforcement using military equipment moved in on protestors opposed to the construction of an oil pipeline in North Dakota on Thursday. The pipeline has been a source of controversy and conflict for months, with activists and tribe members pushing to halt installation and arguing that it would endanger the environment and defile land held sacred by the local Native American community.

As of Thursday afternoon, authorities said that the Dakota Access pipeline construction site had been cleared, the Associated Press reported.

The protestors were being accused of trespassing on private property, setting up camps at the construction site, and blocking roads, CNN reported. The North Dakota Department of Emergency Services has solicited support from law enforcement agencies in seven other states — Wisconsin, South Dakota, Minnesota, Indiana, Nebraska, Wyoming, and Ohio — to remove protestors in order to continue building the 1,172-mile pipeline.

This is what that effort looked like on Thursday.

NDES spokeswoman Cecily Fong told ATTN: that the situation escalated since the evacuation operation started around 11 a.m. on Thursday. She said that some protestors have thrown rocks at law enforcement officials and that there have been "a handful" of injuries. Protestors allegedly set fire to a bridge and blocked roads by abandoning their vehicles in an effort to impede law enforcement.

"We’ve used a variety of tools and tactics to get them to move, and certainly, initially, it was a peaceful movement south toward [the protestor's encampment] and, as they’ve been moving, I would say it's escalated," Fong said.

Authorities have used tear gas, sound cannons, and bean bag rounds to disperse the protestors, Fong said. She added that at least 16 arrests have been made but could not confirm the reasons for the arrests.

Protestors have expressed anger over the enforcement effort, which they see as an excessive move by a militarized police force that could endanger children and women engaged in a peaceful protest. A spokesperson for the Standing Rock Sioux Tribe told NBC News that "the tribe had asked the U.S. Department of Justice to intervene in the escalating situation with law enforcement."

Why are people protesting the pipeline?

Energy Transfer Partners - daplpipelinefacts.com

The Dakota Access pipeline is a $3.7 billion project that was approved by the U.S. Army Corps of Engineers and is being developed by the oil company Energy Transfer Partners. Pending the pipeline's completion, it would transfer about 470,000 barrels of crude oil from North Dakota to Illinois each day, according to Energy Transfer Partners.

The Standing Rock Sioux Tribe has opposed the pipeline because they say it would desecrate sacred burial grounds and threaten the tribe's "environmental and economic well-being." The concern is that the pipeline could possibly leak gas and contaminate land and water supplies. The tribe also worries that the pipeline will "damage and destroy sites of great historic, religious, and cultural significance to the Tribe," according to a lawsuit the tribe filed against the Corps in July.