North Dakota’s Republican senator on Wednesday blamed violent clashes between Dakota Access Pipeline protesters and law enforcement on President Barack Obama’s reluctance to approve the controversial project.

“The ongoing protest activities ― which at times have turned violent ― are being prolonged and intensified by the Obama administration’s refusal to approve the final remaining easement at Lake Oahe,” Sen. John Hoeven said on the Senate floor.

A permit to build beneath Lake Oahe section of the Missouri River is the unfinished piece of Energy Transfer Partners’ 1,172-mile pipeline from North Dakota to Illinois. The Obama administration withheld the permit in September after ordering a review of the application process and agreeing to consider a Native American tribe’s concerns that the pipeline threatens native land and drinking water.

“This inaction has inflamed tensions, strained state and local resources, and, most importantly, is needlessly putting people at risk ― including tribal members, protestors, law enforcement officers, construction workers, and area residents ― our farmers and ranchers who live and work in the area,” Hoeven said.

Hoeven said the pipeline is 98-percent complete in North Dakota, and 86- percent finished overall. Thousands of miles of pipelines crisscross the country already, said Hoeven, who argued that pipelines are safer than other methods of transporting oil.

“It’s past time to get this issue resolved,” Hoeven said.

The permit delay may be the last hope for the Standing Rock Sioux. The tribe contends the pipeline violates federal antiquities laws and an 1851 treaty.

Hoeven’s comments come as officials ratchet up opposition to the protesters, who call themselves water protectors, and the camp they’ve occupied for months on federal land.

On Tuesday, the Morton County Sheriff’s Department indicated that it would block delivery of food, medicine and other supplies to protesters who defy orders to leave the Oceti Sakowin camp. Gov. Jack Dalrymple on Monday ordered mandatory evacuation of the camp because of a predicted strong winter storm.

The first blow to the camp’s security was an announcement last week that the U.S. Army Corps of Engineers would shut an area to the public that includes the main camp. The corps said its decision was based on growing violence between police and protesters and the onset of cold weather.

The Standing Rock Sioux and their supporters, thus far, have refused to leave.

Hoeven, along with the governor and the state’s congressman, Rep. Kevin Cramer (R), have previously called on Obama to deploy federal law enforcement personnel to subdue the protest activity.

“We recommend you provide federal law enforcement resources immediately to state and local agencies in order to maintain public safety, which has been threatened by ongoing ― and oftentimes violent ― protest activity,” the politicians wrote in a Nov. 23 letter to the president. “These resources are essential to prevent further destruction on and surrounding federal lands.”