Rights group Amnesty International became the latest to wade into the controversy over the Dakota Access pipeline, alleging excessive force by area police.

The sheriff's department in Morton County, N.D., is facing questions over its decision to use water cannons and other non-lethal means to disperse activists protesting against the construction of the Dakota Access pipeline.

In a letter to the Morton Country Sheriff Kyle Kirchmeier, Amnesty International said law enforcement personnel may have stepped out of line during weekend efforts to quell the demonstrations.

"Where a small minority tries to turn a peaceful assembly into a violent one, law enforcement officials should protect the peaceful protesters and not use the violent acts of a few as a pretext to restrict or impede the exercise of the rights of a majority," the letter read.

The United Nations in the past has expressed similar concerns about human rights issues in North Dakota. Regional law enforcement officials defended their actions, saying some protesters were using aggression against police officers trying to keep the peace.

North Dakota's governor has been relatively silent on the ongoing protests against the pipeline. Last week, he pressed the White House to work to resolve any outstanding issues on the project in the interest of public safety.

"Further delays simply prolong the risks to public safety, prolong the hardships endured by area residents and increase costs incurred by the state of North Dakota and Morton County," Gov. Jack Dalrymple said in a statement.

The U.S. Army Corps of Engineers said last week that further review was needed in order to assess tribal interests associated with the construction of the last few hundred feet of the pipeline. The decision means pipeline consortium Energy Transfer Partners is delayed in the construction of a $3.7 billion pipeline meant to carry hundreds of thousands of barrels of oil from North Dakota oil fields to Illinois and then onto the southern U.S. coast.

The project consortium filed a legal challenge against alleged "political interference" in the project

The Dakota Access pipeline could carry up to half of what North Dakota produces and the pipeline consortium said that would reduce shipment by rail, which carries its own risks. At least 40 people were killed in Lac-Megantic, Quebec, in the 2013 derailment of a train carrying tankers of crude oil from North Dakota to Canadian refineries.

The last few hundred feet of construction requires drilling under the Missouri River.