Twenty-eight protesters against the Dakota Access oil pipeline were arrested west of Mandan, North Dakota, during a day in which activists held demonstrations nationwide.
Morton County sheriff's spokesman Rob Keller says about 400 protesters put a pickup truck and tree branches on BNSF Railway tracks Tuesday near a pipeline work staging area. The railroad says trains were delayed three hours.
Officers in riot gear used pepper spray and in one instance a stun gun against protesters who refused to leave.
Activists called for demonstrations at Army Corps of Engineers offices and at banks financing the pipeline construction. Protests were reported across the country, from California to Vermont.
The $3.8 billion pipeline is to carry North Dakota oil to a shipping point in Illinois. Opponents worry it will harm the environment.