The U.S. Army Corps of Engineers on Friday completed more than a year of additional study of the North Dakota-to-Illinois Dakota Access oil pipeline, saying the work substantiated its earlier determination that the pipeline poses no significant environmental threats.

President Trump on Tuesday gave the go-ahead for construction of two controversial oil pipelines, the Keystone XL and the Dakota Access, a White House official tells NPR's Tamara Keith.

Opponents of the Dakota Access Pipeline say roughly 40 people were arrested Saturday during a public demonstration along the construction project's route in southeast Iowa.