Gray wolves in the Northern Rockies will be removed from the endangered species list, following a 13-year restoration effort that helped the animal's population soar, federal officials said Thursday.

An estimated 1,500 wolves now roam Wyoming, Idaho and Montana. That represents a dramatic turnaround for a predator that was largely exterminated in the United States outside of Alaska in the early 20th century.

"Gray wolves in the Northern Rocky Mountains are thriving and no longer require the protection of the Endangered Species Act," said Interior Deputy Secretary Lynn Scarlett. "The wolf's recovery in the Northern Rocky Mountains is a conservation success story."

The restoration effort, however, has been unpopular with ranchers and many others in the three states since it began in the mid-1990s, and today some state leaders want the population thinned significantly.

The states could allow hunters to target the animals as soon as this fall. That angers environmental groups, which plan to sue over the delisting and say it's too soon to remove federal protection.

"The enduring hostility to wolves still exists," said Earthjustice attorney Doug Honnold, who is preparing the lawsuit. "We're going to have hundreds of wolves killed under state management. It's a sad day for our wolves."

The wolf will be formally removed from the endangered species list 30 days after the federal government's decision is published in the Federal Register, which is expected next week.