Construction of the Dakota Access Pipeline will be halted, MSNBC reported Sunday afternoon, a major victory for the Standing Rock Sioux tribe and the thousands who protested the building of the crude oil pipeline that extends over four states and through sacred Rock Sioux land.

The secretary of the U.S. Army Corps of Engineers on Sunday told the head of the Standing Rock Sioux tribe, Dave Archambault II, that the government would deny a federal permit needed for the pipeline to cross under Lake Oahe in North Dakota.

"I'm thankful that there were some leaders in the federal government that realized that some things were not right," Archambault told MSNBC.

"They heard our voices and had the initiative to make the right decisions."

The announcement comes one week after the Army Corps ordered protesters to vacate their camp site by Dec. 5. The billion-dollar project, backed by Energy Transfer Partners LP, was set to span 1,172 miles and four states from North Dakota to Iowa and carry 570,000 barrels of crude oil per day.

ETP applied to build the pipeline in December 2014 and received final approval for the project in March 2016, but the Rock Sioux tribe waged a battle to keep it from happening and sued the Army Corps in late July.

It paid off.

Sen. Bernie Sanders hailed the announcement.

"I appreciate very much President Obama listening to the Native American people and millions of others who believe this pipeline should not be built,” Sanders wrote. “In the year 2016, we should not continue to trample on Native American sovereignty. We should not endanger the water supply of millions of people. We should not become more dependent on fossil fuel and accelerate the planetary crisis of climate change. Our job now is to transform our energy system away from fossil fuels, not to produce more greenhouse gas emissions."

U.S. Attorney General Loretta Lynch released a statement saying her office would continue to monitor the situation and "stand ready to provide resources to help all those who can play a constructive role in easing tensions.

"The department remains committed to supporting local law enforcement, defending protestors’ constitutional right to free speech and fostering thoughtful dialogue on the matter," Lynch said. "We recognize the strong feelings that exist in connection with this issue, but it is imperative that all parties express their views peacefully and join us in support of a deliberate and reasonable process for de-escalation and healing."

A celebration erupted at the main protest camp in Cannon Ball, North Dakota, where the Standing Rock Sioux tribe and others have been protesting the 1,172-mile Dakota Access Pipeline for months.

The line had been complete except for a segment planned to run under Lake Oahe, a reservoir formed by a dam on the Missouri River.

That stretch required an easement from federal authorities, which delayed a decision on the permit twice, in an effort to consult further with the tribe.

"The Army will not grant an easement to cross Lake Oahe at the proposed location based on the current record," a statement from the U.S. Army said.

Protesters have said the project could contaminate the water supply and damage sacred tribal lands.

"I hope they follow through here with this. They haven't been following the law all along. So we'll see - but this is a victory today for our people and our water," said Gerad Kipp, 44, an irrigation engineer from Missoula, Montana and a Native American.

Archambault thanked activists for their support in the protest effort.

"The Standing Rock Sioux Tribe and all of Indian Country will be forever grateful to the Obama Administration for this historic decision," he said.

"We want to thank everyone who played a role in advocating for this cause. We thank the tribal youth who initiated this movement."

Jo-Ellen Darcy, the Army's Assistant Secretary for Civil Works, said in a statement the decision was based on a need to explore alternate routes for the pipeline. She said the best way to move forward was to explore alternate routes.

Protest organizers had for months argued that crossing the Missouri River adjacent to the Standing Rock Sioux Reservation presented a danger to their water source. Protests grew over the months, with hundreds of veterans flocking to the camp in recent days to stand against what they say are aggressive tactics from law enforcement.

It is unclear what the pipeline route will be, however, and any route would still likely need to cross the Missouri River, probably upstream of Lake Oahe and closer to the state capital of Bismarck. Many pipelines travel under U.S. waterways already, and pipe is considered a safer way to transport crude oil than rail.

North Dakota Senator Heidi Heitkamp, a Democrat, nodded to the fact that next steps remain unclear, saying in a statement Sunday that the pipeline "still remains in limbo."

What is also unclear as well is whether the incoming administration of Donald Trump may consider taking up Energy Transfer Partners' request yet again, and approving it. Trump's transition team last week said that he was supportive of the line, in addition to other pipeline development.

"We're hopeful that when the Trump administration takes office it will look at all of the priorities it has and that putting at risk the water supply of the Standing Rock Sioux isn't on their list," said Michael Brune, executive director of the Sierra Club

A spokesperson for Energy Transfer Partners could not immediately be reached for comment.

Reuters contributed to this report.