(CNN) As outrage grows over the killing of Cecil the lion, Zimbabwe has called on the United States to extradite the American dentist who shot the prized big cat.

Zimbabwe has started extradition proceedings and hopes the United States will cooperate, said Oppah Muchinguri, the African nation's environment minister.

Walter Palmer "had a well-orchestrated agenda which would tarnish the image of Zimbabwe and further strain the relationship between Zimbabwe and the U.S., Muchinguri said.

Palmer, his professional hunter guide, and the owner of the land where the hunt took place are accused of an illegal hunt under the country's Parks and Wildlife Act, Muchinguri said in a statement.

Palmer is accused of financing an illegal hunt, and he and the professional hunter are also accused of illegally using a crossbow "to conceal the illegal hunt" so they wouldn't alert rangers on patrol, she said.

The landowner allegedly allowed the hunt to be conducted without a lion quota and without the necessary permit, Muchinguri said.

"The professional hunter, client and land owner were therefore all engaged in poaching of the lion," she said.

She added, "This must be condemned in the strongest possible terms by all genuine, animal-loving conservationists who believe in sustainable utilization of natural resources."

JUST WATCHED American dentist says he regrets killing famed lion Replay More Videos ... MUST WATCH American dentist says he regrets killing famed lion 03:47

Palmer, from Minnesota, has said he relied on the expertise of local guides "to ensure a legal hunt."

"I had no idea that the lion I took was a known, local favorite, was collared and part of a study until the end of the hunt," Palmer said in a statement Tuesday.

He allegedly paid $50,000 in early July to hunt the lion with a crossbow near Hwange National Park in western Zimbabwe.

Cecil -- a major tourist draw at Hwange -- was lured out of the park sanctuary with a dead animal on top of a vehicle, according to the Zimbabwe Conservation Task Force

The 13-year-old lion, recognizable by the black streaks in his mane, suffered a slow death , the conservation group said.

A Palmer representative contacts U.S. game officials

Palmer's whereabouts are publicly unknown amid the uproar over the hunt, though his representative contacted the U.S. Fish and Wildlife Service on Friday, the agency said.

The U.S. Fish and Wildlife Service is investigating the circumstances of the lion's death.

"The service's investigation is ongoing and appreciates that Dr. Palmer's representative voluntarily reached out to the service," the agency said, offering no detail about the correspondence.

Late yesterday we were voluntarily contacted by a rep of Dr. Palmer. We appreciate the cooperation, investigation is ongoing. #CecilTheLion — US Fish and Wildlife (@USFWS) July 31, 2015

This week, the Fish and Wildlife Service made a public appeal to Palmer, asking him to contact the agency: "That investigation will take us wherever the facts lead. At this point in time, however, multiple efforts to contact Dr. Walter Palmer have been unsuccessful," said Edward Grace, the Fish and Wildlife Service's deputy chief of law enforcement. "We ask that Dr. Palmer or his representative contact us immediately."

Minister: Taking this issue seriously

Meanwhile, a White House petition requesting that Palmer be extradited to Zimbabwe may receive a response from the Obama administration.

The petition needed to receive 100,000 signatures by August 27 to get a response. It had more than 175,000 signatures by Friday afternoon.

Muchinguri said that there was also much outcry in Zimbabwe and that nearly 500,000 people via Facebook had called for Palmer's extradition.

"We are taking this issue seriously," she said, adding that Palmer should be tried in Zimbabwe.

Hundreds of protesters have gathered this week outside Palmer's dental practice in Bloomington, Minnesota, CNN affiliate WCCO-TV in Minneapolis reported.

Feds mum on extradition request

The U.S. State Department said that as a matter of policy, it would not comment on specific extradition requests.

JUST WATCHED Cecil the lion's death renews calls for hunting ban Replay More Videos ... MUST WATCH Cecil the lion's death renews calls for hunting ban 04:24

"Privacy considerations prevent us from commenting further on the status of the U.S. citizen allegedly involved," it said. "For inquiries regarding any law enforcement aspects of the case, we refer you to the government of Zimbabwe or the Department of Justice."

The Department of Justice declined to comment on the extradition request.

Investigations indicate the killing of Cecil was illegal because the landowner "was not allocated a lion on his hunting quota for 2015," said a statement from the Zimbabwe Parks and Wildlife Management Authority.

Cecil lovers send in donations

The lion's death has seen a huge boost in donations for conservation efforts, according to Oxford University's Wildlife Conservation Research Unit. Its researchers had been tracking Cecil since 2008.

So far, $470,000 has been raised, enough to fund research into lion conservation in Hwange National Park for two years, it said. Two U.S. philanthropists, Tom Kaplan and his wife, Daphne Recanati Kaplan, have pledged to match any further donations, up to $100,000, it added.

Cecil's cubs likely to survive

Meanwhile, Cecil's cubs are likely to survive, even in the wake of the animal's death, according to one scientist who had been studying the lion.

The cubs are alive and are likely to be defended by Cecil's brother, Jericho, who may have fathered some cubs himself, said professor David Macdonald, director of Oxford's Wildlife Conservation Research Unit.

The cubs are not being tracked, and conservationists would have to find the adult females to find the cubs, Macdonald said.

Male coalitions -- often brothers -- oversee prides of females in lion society, and any threat is posed by external, incoming male lions, Macdonald said.