Two American hunters are one big step closer to legally killing a pair of black rhinos in Namibia and bringing their body parts home as trophies. On Thursday, the U.S. Fish and Wildlife Service announced online that it was approving the hunters' requests to import trophies from two upcoming hunts sanctioned by the Namibian government.

After sifting through thousands of citizen comments over the past several months, the U.S. federal agency defended its decision by saying the hunts, which are slated to raise money for conservation, are part of Namibia’s “science-based management strategy for black rhinos.”

In short, the agency said the permit requests meet the legal standard of allowing limited hunting of an endangered species to benefit its conservation overall. There are about 4,000 to 5,000 black rhinos left in the world, down from 70,000 in the 1960s. (See "Rhino Wars" in National Geographic magazine.)

Hunter and reality TV host Corey Knowlton had applied for an import permit following his $350,000 winning bid for a hunting permit in Namibia at an auction last year held by the Dallas Safari Club. Hunter Michael Luzich of Las Vegas had also applied for a permit to import a trophy from another hunt in the African country.

More than 135,000 people signed public petitions against the hunt or sent private comments to the agency, an unprecedented level of public interest. The Fish and Wildlife Service has declined to share the nature of the individual comments, but several animal advocacy groups have spoken out against the ruling.

The animal rights group People for the Ethical Treatment of Animals “will be filing a lawsuit over this outrageous decision to allow two sports hunters to bring back the bodies of animals shot in cold blood to decorate their trophy walls," PETA Foundation Deputy General Counsel Delcianna Winders said in a statement.

"These permits are fundamentally inconsistent with the purpose of the Endangered Species Act, which is to conserve endangered species, not to authorize their slaughter."

Wayne Pacelle, president and CEO of the Humane Society of the United States, calls the agency’s decision “the worst sort of mixed message to give a green light to American trophy hunters to kill rhinos for their heads.”

But the Fish and Wildlife Service says, “Money accrued from trophy hunting of black rhinos has been used to fund annual black rhino counts, improve rhino crime investigation and prosecution, and ensure the traceability of all rhino horn owned by Namibia.”