The U.S. Forest Service says it's investigating after Idaho officials reported inadvertently putting tracking collars on four wolves during recent helicopter flights into a central Idaho wilderness restricted to putting collars on elk.

Idaho Department of Fish and Game Deputy Director Ed Schriever in a statement Wednesday said the agency didn't clearly communicate to one of the helicopter crews entering the Frank Church River of No Return Wilderness. "We will refine our procedures to make sure this doesn't happen again," Schriever said.

Environmental groups said they are concerned that Fish and Game is aiming to gather information to justify killing wolves in the area.

Forest Service spokesman Wade Muehlhof said the agency is interested in what went wrong that allowed the capture and collaring of the four wolves.

"Collaring wolves is not part of the authorization of the Forest Service," he said. "This is not what was agreed to."

The state manages wildlife, and the U.S. Forest Service oversees the River of No Return Wilderness. The federal agency on Jan. 6 approved Fish and Game's request to use helicopters in the area. The flights took place the following three days, Fish and Game said.

Fish and Game said the number of helicopter landings in the wilderness remained within the limits of the agreement, and that the agency succeeded in its objective of putting collars on 60 elk.

The agency said the collars will work for up to three years. The locations of the elk will be monitored remotely, and workers notified of a death by a signal that is stationary would fly in to try to determine the cause.

Three environmental groups — Wilderness Watch, Western Watersheds Project and Friends of the Clearwater — sued in federal court last week to stop the helicopter flights into the wilderness. The groups contend the flights violate the Wilderness Act and other environmental laws. Wilderness areas generally don't allow mechanized equipment.

Attorney Tim Presso with Earthjustice said putting tracking collars on wolves created additional concerns. "Idaho used the opportunity to put collars on wolves in the wilderness, which of course gives rise to the very real possibility that those collars will be used by the state for the purpose of killing them," he said.

Presso said the lawsuit will move forward even though the flights have already been made.

The environmentalists' fears about wolves come as Idaho officials hope to see the number of predators dwindle. They created a Wolf Depredation Control Board in 2014 intended to reduce the wolf population.

In April 2014, the state had an estimated 770 wolves in 104 packs, according to the U.S. Fish and Wildlife Service.