Walter Palmer, the US dentist and big game hunter who killed Cecil the lion in Zimbabwe, has written a letter to his patients apologising for the disruption to their treatment while the international furore continues.

Palmer's River Bluff Dental practice in Minnesota has remained closed since it was revealed this week that he was the tourist who shot dead Cecil, a well-known lion in the Hwange National Park.

His actions have attracted a blaze of international condemnation and commentary that has, at times, turned threatening.

In the letter, addressed to his "valued patients", Palmer once again stated that he thought the hunt was legal and that the proper hunting permits had been obtained.

He wrote that the backlash was for reasons "that have nothing to do with my profession or the care I provide for you".

He also explained to his patients that he had been hunting since he was a child in North Dakota, but did not discuss his hobby with his patients because he realised the topic could be divisive and emotionally charged.

"I understand and respect that not everyone shares the same views on hunting," he wrote to his patients.

"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. I relied on the expertise of my local professional guides to ensure a legal hunt.

"Again, I deeply regret that my pursuit of an activity I love and practice responsibly and legally resulted in the taking of this lion.

"That was never my intention. The media interest in this matter – along with a substantial number of comments and calls from people who are angered by this situation and by the practice of hunting in general – has disrupted our business and our ability to see our patients.

"For that disruption, I apologize profoundly for this inconvenience and promise you that we will do our best to resume normal operations as soon as possible."

Palmer said his patients would be referred to other dentists for treatment while the practice remained closed, before signing off by thanking his patients for their support.

River Bluff Dental has taken down its Facebook page and website in the midst of the controversy.

Red roses and more than a dozen stuffed animals have been laid outside the locked front door of his dental practice as a memorial to Cecil.

It has been alleged that, during the hunt in Zimbabwe, Cecil was lured out of the national park at night using bait, before Palmer shot the lion with a bow and arrow.

The next day, Cecil was found wounded by the hunters and killed, before being beheaded and skinned.