Cecil was one of Africa’s best known lions. He was found skinned and headless on the outskirts of the park. Traces of his last movements show when he was tricked into leaving the park and shot with a bow and arrow. After they hit him, the hunters tracked the dying lion for 40 hours before they killed it with a rifle. Photo: jewishbusinessnews.com

Oppah Muchinguri told a news conference that Walter Palmer, 55, was a “foreign poacher” and said she understood Zimbabwe’s prosecutor general had started the process to have him extradited.

“Unfortunately it was too late to apprehend the foreign poacher as he had already absconded to his country of origin,” she told a news conference on Friday. “We are appealing to the responsible authorities for his extradition to Zimbabwe so that he be made accountable.”

Muchinguri’s remarks come as the White House faces mounting pressure to address a petition for Palmer’s extradition to Zimbabwe.

The petition has collected more than 160,000 signatures since it was launched last Tuesday, exceeding its stated goal of reaching 100,000 signatures by 27 August.

“We urge the Secretary of State John Kerry and the Attorney General Loretta Lynch to fully cooperate with the Zimbabwe authorities and to extradite Walter Palmer promptly at the Zimbabwe government’s request,” the petition read.

A White House spokesman said on Thursday that the Obama administration will respond to the petition, which it must to do within 60 days.

A separate Care2 petition condemning Palmer and demanding justice for Cecil has racked up nearly one million signatures from people across the world.

A bilateral extradition treaty between the US and Zimbabwe has been in effect since April 2000 in cases where an individual is charged with what would be a criminal offence in both countries.

The US Fish and Wildlife Service (USFWS) said on Thursday it was investigating the illegal killing of the lion by the Minnesota dentist and whether any US laws were broken. The service was “voluntarily” contacted by a representative of Palmer on Friday after “multiple” attempts to reach him were unsuccessful, spokesperson Vanessa Kauffman said. Kauffman confirmed that the Service’s investigation was ongoing.

Palmer, a keen big game hunter who posts pictures of his kills on social media, is said to have paid around $50,000 (£32,000) for the chance to kill Cecil, a protected 13-year-old lion famous for his black-fringed mane, in Zimbabwe’s Hwange national park earlier this month.

The lion was reportedly lured to outside the park’s boundaries and wounded with a bow and arrow, before being shot dead hours later.

Edward Grace, the USFWS deputy chief of law enforcement, said the service was investigating the circumstances surrounding the killing of Cecil. “That investigation will take us wherever the facts lead,” he said, adding that the service “will assist Zimbabwe officials in whatever manner requested”.

Grace said: “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 savanna for generations to come.”

The USFWS proposed listing African lions as threatened under the Endangered Species Act last October.

Grace also urged Palmer “or his representative [to] contact us immediately”, noting that “multiple efforts to contact Dr Walter Palmer have been unsuccessful”.

Palmer on Thursday wrote to to his patients to say he he was sorry for killing the beast, but described hunting as his passion.

“I don’t often talk about hunting with my patients because it can be a divisive and emotionally charged topic,” he wrote. “I understand and respect that not everyone shares the same views on hunting.”

Repeating his claim made in an earlier statement, Palmer said he had no idea the lion he killed was “a known local favourite” and said he would assist the Zimbabwean authorities.

The dentist has a kill list of 43 different animals including a polar bear, a mountain lion, an elephant and an African lion he killed in 2005, according to records obtained by the Minneapolis Star Tribune.