The U.S. Department of the Interior says it needs at least 10 more weeks to decide whether polar bears should be listed as a threatened species.

Assistant Interior Secretary Lyle Laverty replied Thursday to a lawsuit filed last month by three conservation groups opposing the government's delay, which is now past the four-month mark.

The Center for Biological Diversity, the Natural Resources Defence Council and Greenpeace filed the lawsuit with the U.S. Federal Court in San Francisco in March.

Laverty said Thursday that the proposed polar bear listing raises "significant and complex factual and legal issues," the Associated Press reported.

The U.S. Fish and Wildlife Service has been reviewing the possibility of listing polar bears as a threatened species under the Endangered Species Act, prompted by concerns by conservation groups and scientists that global warming is shrinking the bears' habitats on the Arctic sea ice.

Listing polar bears as threatened would require U.S. federal agencies to ensure their activities do not jeopardize the bears or the sea ice on which they live.

If the government proceeds with a threatened listing, it could affect oil and gas exploration, commercial shipping or even releases of pollution that might affect climate.

Such a decision could also affect Canadian outfitters in Nunavut and the Northwest Territories, who profit from Americans coming north on sport hunts.

Critics, including the Nunavut government and U.S. sport hunters' associations, have argued that a threatened status could lead to a ban on polar bear trophy imports, hurting the sport hunting industry in Canada's North.

A decision on the matter was originally due Jan. 9. That deadline was extended by one month, but no decision has been announced to date.

Kassie Siegel, a spokeswoman for the Center for Biological Diversity, says the request for more time should be rejected.

With files from the Associated Press