The law enforcement arm of the US Fish & Wildlife Service is trying to reach the dentist who killed a protected lion while on a guided hunt in Zimbabwe.

The agency is investigating circumstances surrounding the death of a lion, named Cecil, Fish & Wildlife law enforcement deputy chief Edward Grace said.

Cecil was drawn from a wildlife preserve and shot by American hunter Walter James Palmer on July 1.

Dr Palmer is believed to have shot the lion with a bow and then the wounded cat was tracked for 40 hours before he killed it with a gun.

Mr Grace says multiple efforts to contact the dentist were unsuccessful and "we ask that Dr Palmer or his representative contact us immediately".

A public relations professional released a statement on Tuesday from Dr Palmer, who said he was with professional guides and thought the hunt was legal.

On Thursday, it was revealed that Safari Club International has suspended Dr Palmer's membership and that the organisation wants a "full and thorough investigation" into the lion's death.

The club, which promotes big-game hunting worldwide, issued a statement late on Wednesday saying memberships for Walter Palmer and his guide in Zimbabwe, Theo Bronkhorst, will be on hiatus until investigations are complete.

Bronkhorst is facing criminal charges in Zimbabwe over the July 1 killing of the beloved Cecil.

The Safari Club says "those who intentionally take wildlife illegally should be prosecuted and punished to the maximum extent allowed by law".

Meanwhile passionate animal activist and Golden Girls actress Betty White had harsh words for Dr Palmer.

"You don't want to hear some of the things I want to do to that man," the 93-year-old actress said.

"It's such a heartbreaker. You can't even talk about it, and to see this king of the jungle and personifying it in every way, this gorgeous creature. How can somebody do that?"

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