More farm animals have been killed in south central North Dakota's Morton and Sioux counties.
The North Dakota Stockmen's Association says four bison were butchered in a pasture, and two cows in another pasture were killed and burned.
Over the past five weeks, more than a dozen animals in the region have been killed or injured, and nearly three dozen others have been reported missing.
The incidents are near the site where people have gathered to protest the Dakota Access oil pipeline, but the Stockmen's says there is no evidence that there is any connection.
The rancher group is offering a reward of up to $14,000 for information that helps crack the cases.