The US dentist who sparked international outrage when he killed Cecil the lion during a hunting trip to Zimbabwe returned to work Tuesday after six weeks in hiding, local media reported.

Walter Palmer entered his Bloomington, Minnesota, dental practice without a word amid a crowd of protesters and reporters, according to the Minneapolis Star Tribune newspaper.

A photo tweeted by broadcaster CBS meanwhile showed the 55-year-old, casually dressed in a dark polo shirt, surrounded by people scrambling to take pictures on their cell phones.

Zimbabwe has asked the United States to extradite Palmer to face charges over the July hunt.

The Star Tribune reported there was a small police presence on hand outside the dental practice at daybreak as the first employees arrived. However, there were no reports of scuffles.  

In his first interview since the uproar, Palmer told the newspaper over the weekend that he and the others in his party had no clue that the animal they were hunting was the revered feline that has been a well-known attraction at the Hwange National Park.

He also maintained he thought that the hunt, during which he was armed with a powerful crossbow, was legal.

Palmer declined to say whether he would abide by any request to return to Zimbabwe over legal allegations, and an attorney present for the interview added that there had been "no official allegations that he's done anything wrong."

Cecil had been wearing a tracking collar as part of an Oxford University research project. But Palmer said he had been unable to see the device in the night and under the animal's mane, adding that it was not illegal to kill lions with collars.

In other comments, Palmer said the ordeal had been particularly difficult for his wife and daughter, who had been threatened on social media.