By Madison Park

WASHINGTON — (CNN) The US Army Corps of Engineers has delayed the construction of the controversial Dakota Access Pipeline to hold further “discussion and analysis” with the Standing Rock Sioux Tribe, which has vehemently opposed the project.

Protests have simmered for months, spawning bitter clashes over the Dakota Access Pipeline, a 1,172-mile oil pipeline currently under construction that would span from North Dakota to Illinois.

The pipeline’s developer sought permission from the Army Corps to tunnel under the Missouri River in Lake Oahe, North Dakota, in order to complete the project.

The Standing Rock Sioux Tribe, which relies on the lake and river for its drinking water, has objected over environmental concerns. It contends that digging the pipeline under the Missouri River would affect the tribe’s drinking water supply and put communities living downstream “at risk for contamination by crude oil leaks and spills.”

On Monday, the Army Corps of Engineers halted further construction on and around the lake, because it “has not made a final decision on whether to grant an easement,” according to its statement. Further review was needed in consult with the tribe, it said.

“The Army is mindful of the history of the Great Sioux Nation’s repeated dispossessions, including those to support water-resources projects,” according to a letter sent to the tribe by Jo-Ellen Darcy, the Assistant Secretary of the Army (Civil Works). “This history compels great caution and respect in considering the concerns that the Standing Rock Sioux Tribe has raised regarding the proposed crossing of Lake Oahe.”

The Army Corps said it would consult with the tribe regarding “potential conditions on an easement” that would reduce risks of spills and protect the water supply. It also pledged to do complete the review “expeditiously.”

Delay decried by pipeline backers

But the companies behind the Dakota Access Pipeline slammed the latest decision as “lacking legal or factual justification.”

“The Corps knows full well that it is seeking additional consultation with a party [Standing Rock Sioux Tribe] that has steadfastly refused to consult,” according to a joint statement from Energy Transfer Partners and Sunonco Logistics Partners.

The companies stated that they would “vigorously pursue its legal rights.”

Last Tuesday, Energy Transfer Partners announced that it had completed the pipeline on each side of Lake Oahe and was preparing to drill as it awaited the easement from the Army Corps. The project had previously received a permit from the Army Corps to tunnel under the lake, it said.

Kelcy Warren, Energy Transfer Partners’ CEO, decried the decision as “motivated purely by politics at the expense of a company that has done nothing but play by the rules it was given.”

Dakota Access is a $3.7 billion project that backers have touted as the safest and most efficient way to transport oil, rather than using rail or trucks. Its proponents also say the pipeline could help the US become less dependent on importing energy from foreign countries.

Tribe says pipeline harms more than environment

Meanwhile, the Standing Rock Sioux Tribe said the Army Corps’ announcement wasn’t 100 percent what it had sought, but showed that its concerns had been heard.

“We are encouraged and know that the peaceful prayer and demonstration at Standing Rock have powerfully brought to light the unjust narrative suffered by tribal nations and Native Americans across the country,” said Standing Rock Sioux Chairman David Archambault II in a statement.

In addition to environmental concerns, the tribe has contended that the Dakota Access Pipeline threatens its members’ economic well being, and its burial and prayer sites.

Multiple groups have joined the protests. Throughout the months-long standoff, activists have routinely destroyed construction equipment as part of their protest.

Archambault had told CNN previously that his tribe will settle for nothing less than stopping the pipeline’s construction.

“We’re not opposed to energy independence. We’re not opposed to economic development,” he said. “The problem we have — and this is a long history of problems that evolved over time — is where the federal government or corporations take advantage of indigenous lands and indigenous rights.”

The-CNN-Wire ™ & © 2016 Cable News Network, Inc., a Time Warner Company. All rights reserved. (PHOTO: CNN)