Assistant secretary for civil works Jo-Ellen Darcy announced the decision on Sunday, with the army saying it was based on “a need to explore alternate routes” for the crossing.

“Although we have had continuing discussion and exchanges of new information with the Standing Rock Sioux and Dakota Access, it’s clear that there’s more work to do,” Darcy said in a statement. “The best way to complete that work responsibly and expeditiously is to explore alternate routes for the pipeline crossing.”

The army corps will undertake an environmental impact statement and look for alternative routes, the tribe said in its own announcement.