BILLINGS, Mont. (AP) — Environmental groups say they have filed a lawsuit to block the federal government from allowing states to kill more endangered wolves in the Northern Rockies.

Federal officials want to empower state wildlife agencies to kill off packs of wolves in Idaho, Wyoming and Montana that have a "major impact" on big game herds, particularly elk.

Environmental groups claim as many as 600 of the region's 1,500 wolves could be killed. Seven groups announced Monday they had filed a lawsuit in U.S. District court in Missoula to stop the rule from being adopted next month.

The top federal wolf biologist, Ed Bangs with the U.S. Fish and Wildlife Service, says far fewer wolves would be killed than the groups claim.