SPOKANE, Wash. (AP) — The reward for information regarding the killing of two wolves in northeastern Washington state has grown to $20,000, two conservation groups said Monday.

The Center for Biological Diversity and Cascadia Wildlands doubled a previously announced $10,000 reward by Conservation Northwest for information leading to conviction in the killing of the wolves.

Over the weekend, officials for the state Department of Fish and Wildlife announced that two wolves that were being monitored had been found shot to death.

The animals were members of the Smackout and Dirty Shirt packs.

"Poaching wolves or other wildlife is a deplorable crime," said Noah Greenwalt, of the Center for Biological Diversity. "We need people to come forward and help put a stop to the killing of these endangered animals."

Wolves are a protected species across the state of Washington. Poachers can face fines and jail time.

These killings follow the poaching of three wolves in Oregon in the past several months

"Poaching represents a real threat to the recovery of wolves in Washington and elsewhere on the West Coast," said Nick Cady of Cascadia Wildlands.

Gray wolves were hunted to extinction in Washington in the early 1900s. But the animals started migrating into the state in the early 2000s from Idaho and Canada. The first wolf pack was documented by the department in 2008.

At the end of 2016, the state estimated there were a minimum of 115 wolves, 20 packs and 10 successful breeding pairs in the state. All of the documented wolf packs are east of the Cascade Range, mostly in the northeastern corner of the state.

There have been numerous conflicts between wolves and livestock in recent years, and the state has killed 18 problem wolves since 2012, drawing sharp criticism from environmental groups.

Wolves are listed as endangered by the state in the eastern third of Washington and have federal endangered species protection in the western two-thirds of the state.

-- The Associated Press