Walter Palmer, the American dentist who killed Cecil the Lion, could be deported to Zimbabwe to face trial after the country's wildlife minister announced an extradition order for the hunter.
A petition to the White House to extradite Walter Palmer, from Minnesota, hit 160,000 signatures on Thursday, exceeding the 100,000 threshold needed to generate an official response from the Obama administration.
The White House has yet to respond to Zimbabwe's extradition order, although did retweet the news the petition had crossed the 100,000 signature mark.
The lion's death, which occurred in early July, is being investigated by the Zimbabwean authorities and the US Fish and Wildlife Service (USFWS), which said it "shared concern" about the issue.
A USFWS statement read: "We are currently gathering facts about the issue and will assist Zimbabwe officials in whatever manner requested.
"At this point in time, however, multiple efforts to contact Dr Walter Palmer have been unsuccessful.
"It is up to all of us - not just the people of Africa - to ensure that healthy, wild populations of animals continue to roam the savannah for generations to come."
USFWS is investigating the tragic killing of #CecilTheLion. Will go where facts lead. Efforts to contact Dr. Palmer so far unsuccessful.— Dan Ashe (@DirectorDanAshe) July 30, 2015
Palmer, who allegedly paid 50,000 dollars (£31,900) to track and shoot the animal, has said he was unaware the lion was protected and had relied on his local guide to ensure the hunt was legal. He is now in hiding and has closed his dental practice.
Theo Bronkhorst, who is facing criminal charges for his role in Cecil's death, has claimed Palmer wanted to hunt a "very large elephant" after shooting the protected animal.
Palmer, from Minneapolis, shot the lion with a bow and arrow at around 10pm on July 1 after it had been lured outside Hwange National Park by bait. It was not until 9am the next day that the hunters finally tracked down and killed the animal.
The group then skinned and decapitated Cecil, removing his collar so the carcass could not be identified.
The UN general assembly unanimously adopted its first ever resolution aimed at tackling wildlife trafficking on Thursday, which, although is not legally binding, reflects growing opposition to poaching.