BISMARCK, N.D. (AP) — The American Indian tribe leading the legal fight against the Dakota Access oil pipeline is accusing federal officials of being uncooperative as they complete more court-ordered environmental study of the project.

The Standing Rock Sioux is asking a federal judge to order that the tribe be allowed "a meaningful role" in the process. The Cheyenne River Sioux last month made a similar request. If U.S. District Judge James Boasberg grants the requests, it could delay the U.S. Army Corps of Engineers' anticipated April 2 completion of the work.

The Corps has been working sinc...