A polar bear cub nuzzles its mother near Churchill, Man., Nov. 4, 2007. Alaska Gov. Sarah Palin says polar bears are well managed and that their numbers have increased over the last 30 years. (Jonathan Hayward/Canadian Press)

The state of Alaska will sue to challenge the listing of polar bears as a threatened species under the U.S. Endangered Species Act, Gov. Sarah Palin said Wednesday.

Palin said there's insufficient evidence to support the threatened status, which U.S. Interior Secretary Dirk Kempthorne announced on May 14.

Kempthorne said the best available science indicates that the bears' primary habitat — Arctic sea ice — was shrinking and likely to further recede.

But Palin maintained that polar bears are well managed and that their numbers have dramatically increased over the last three decades.

"The state maintains that there is insufficient evidence to support a listing of the polar bear as threatened for any reason at this time," stated a news release issued by Palin's office Wednesday.

"Polar bears are currently well-managed and have dramatically increased over 30 years as a result of conservation measures enacted through international agreements and the Marine Mammal Protection Act. A listing of the polar bear under the [Endangered Species Act] will not provide additional conservation measures."

Conservation groups say the increase in Alaska's polar bear numbers is due to measures that halted overhunting, but that populations are likely to diminish as summer sea ice shrinks.

Palin said her state's attorney general will file a complaint under the U.S. Administrative Procedure Act, arguing that Kempthorne's decision was so arbitrary that it violates the act.

The state will also draft a 60-day notice of intent to sue under the Endangered Species Act, Palin said.

Conservation groups also plan court battle

Meanwhile, American conservation groups also want to take the U.S. government to court over the polar bear's threatened status.

Groups like the Center for Biological Diversity argue that the government had no right to insert a special regulation exempting greenhouse gas emissions and oil and gas industry activities from the rules protecting the now-threatened polar bear species.

"We have filed a court challenge to that special regulation, asserting that it violated the law," Kassie Siegel, a lawyer with the Center for Biological Diversity, told CBC News on Tuesday.

"We hope that it will be overturned in short order and that we will be left with the good parts of the decision while overcoming the bad parts."

The Endangered Species Act was designed to identify threats to a species, then put measures in place to reduce those threats, Siegel said. The exemptions are contradictory and break the law, she argued.

U.S. hunters are also challenging the threatened status in court, as the decision has banned them from bringing home polar bear trophies from hunting trips to places like Canada's North.

With files from the Associated Press