A US dentist who shot dead a famous lion with a crossbow before skinning and beheading the creature has been slated for his actions.

Walter James Palmer, from Minnesota, killed Cecil the lion who was being studied by Oxford University.

Dr Palmer reportedly paid $50,000 (€45,200) to kill Cecil, who was one of the oldest and most famous lions in Zimbabwe, earlier this month.

The Zimbabwe Conservation Task Force said Dr Palmer, a professional hunter and a farm owner, tied a dead animal to a car to lure the lion out of a national park before shooting him. The wounded lion was found 40 hours later and shot dead.

Within hours of the news breaking, Dr Palmer's social media feeds were flooded with blistering attacks -- and threats.

The Twitter and Facebook accounts and website of his dental practice were shut down. Nobody was answering the phone at the dental practice and the voicemail box was overwhelmed.

By late afternoon there were more than 1,800 messages about his practice on review site Yelp and a petition demanding justice for Cecil had garnered nearly 57,000 signatures.

Dr Palmer pleaded guilty in 2008 to US federal charges related to the poaching of a black bear in Wisconsin, the Minneapolis Star Tribune reported.

Dr Palmer has released a statement explaining his actions.

In it he said: "To my knowledge, everything about this trip was legal and properly handled and conducted."

The statement added: "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."

Dr Palmer added he regretted that this "pursuit of an activity I love and practice responsibly and legally resulted in the taking of this lion".

Cecil was lured out of the park he was living in using bait and was shot with a crossbow, according to Mr Rodrigues. He added that the killer paid a Zimbabwean hunter and a game park owner to lure the 13-year-old big cat.

The chairman of the task force, Johnny Rodrigues, said: "The saddest part of all is that now that Cecil is dead, the next lion in the hierarchy, Jericho will most likely kill all Cecil's cubs."

Earlier, a statement issued by the Zimbabwean Parks Authority made no reference to reports that it was a wealthy Spanish or American man had killed Cecil with a bow and arrow after paying a €45,000 fee.

Police said they had arrested two Zimbabwean men on poaching charges, and are looking for Dr Palmer in connection with the same case but said his current whereabouts were unknown. If convicted, they could face up to 15 years in prison.

A British amateur safari enthusiast has posted video online of Cecil the lion.

Paula French, who regularly travels to Africa to watch animals on safari, said she was prompted to post the footage on hearing news of the lion's killing.

“I was sad to hear the news and so put the video up,” she said. Ms French said the lion was filmed during a November 2012 trip to Hwange National Park and identified as Cecil by accompanying rangers.

Professor David Macdonald, who founded the Wildlife Conservation Research Unit at Oxford University, said the death of Cecil would lead to a "cascade" of other deaths.

"The death of one lion is not just the death of one lion - it is a cascade. It has consequences.

"Cecil was the only male so it is highly likely that the incoming males will kill his [Cecil's] offspring."

Prof Macdonald's research aims to solve practical problems with wildlife conservation and environment management to inform policy formation, and he had been observing Cecil just a few months ago.

There are reported to be 30,000 lions left across the whole African continent, but Prof Macdonald warned that this figure, despite being "startlingly low", was likely to be an overestimate.

He added that he hoped there would be a "silver-lining" to Cecil's death by an increase in support for his research.