CANNON BALL, N.D. — The U.S. Army Corps of Engineers said Sunday it won’t grant an easement for the Dakota Access oil pipeline in southern North Dakota, handing a victory to the Standing Rock Sioux tribe and its supporters, who argued the project would threaten the tribe’s water source and cultural sites.

North Dakota’s leaders criticized the decision, with Gov. Jack Dalrymple calling it a “serious mistake” that “prolongs the dangerous situation” of having several hundred protesters who are camped out on federal land during cold, wintry weather. U.S. Rep. Kevin Cramer said it’s a “very chilling signal” for the future of infrastructure in the United States.

The four-state, $3.8 billion project is largely complete except for the now-blocked segment underneath Lake Oahe, a Missouri River reservoir. Assistant Secretary for Civil Works Jo-Ellen Darcy said in a news release that her decision was based on the need to “explore alternate routes” for the pipeline’s crossing. Her full decision doesn’t rule out that it could cross under the reservoir or north of Bismarck.

The company constructing the pipeline, Dallas-based Energy Transfer Partners, released a statement Sunday night slamming the decision as politically motivated and alleging that President Obama’s administration was determined to delay the matter until he leaves office.

President-elect Donald Trump, a pipeline supporter, will take office in January, although it wasn’t immediately clear what steps his administration would be able to take to reverse the Army Corps’ latest decision.

The decision came a day before the government’s deadline for the several hundred people at the Oceti Sakowin, or Seven Council Fires, encampment to leave the federal land.

Earlier Sunday, an organizer with Veterans Stand for Standing Rock said tribal elders had asked the military veterans not to have confrontations with law enforcement officials.