Federal authorities are offering a $2,500 reward for information on the killing of three wolves in northeastern Minnesota.

The U.S. Fish and Wildlife Service says the frozen carcasses were discovered Jan. 22 in a ditch along Minnesota Highway 8 near Floodwood, about 45 miles west of Duluth.

Gray wolves are on the endangered list, and it's illegal to kill them in Minnesota except in self-defense. Otherwise it's punishable by six months in jail and a fine of up to $25,000.

Officials think the wolves were killed elsewhere, then dumped the night before they were found. There's evidence they may have been snared but scientists are still determining how they were killed.

Anyone with information is asked to call the Department of Natural Resources' Turn in Poachers TIP line, 1-800-652-9093.