Piper Hoppe, 10, from Minnetonka, Minnesota, holds a sign at the doorway of River Bluff Dental clinic in protest against the killing of a famous lion in Zimbabwe, in Bloomington, Minnesota, July 29, 2015. [Photo/Agencies]

Palmer said on Tuesday he had hired professional guides who secured hunting permits and deeply regretted taking the lion. He added that he had not been contacted by authorities in Zimbabwe or the United States and would assist in any inquiries.

The Zimbabwe police and government have not commented.

If found guilty, Bronkhorst could be fined $20,000 and possibly jailed for up to 10 years.

The US Fish and Wildlife Service expressed its concern about the killing. "We are currently gathering facts about the issue and will assist Zimbabwe officials in whatever manner requested," said Vanessa Kauffman, a spokeswoman for the government agency. "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."