Image copyright EPA/Facebook Image caption Walter Palmer has faced a huge backlash online over his killing of Cecil the lion

A US dentist who killed a lion in Zimbabwe has apologised to his patients in Minnesota for the disruption caused by the anger directed at him.

Walter Palmer's dental practice in Minneapolis has been closed since he was named as the tourist who shot Cecil, Zimbabwe's most famous lion.

Two Zimbabwean men have been charged over the death and local police say Mr Palmer may also face poaching charges.

He says he thought the hunt was legal and was unaware Cecil was protected.

'Divisive topic'

In a letter sent to his "valued" patients on Tuesday, Mr Palmer said he had been in the news "for reasons that have nothing to do with my profession or the care I provide for you".

He described himself as a "life-long hunter" but said he rarely discussed his passion with patients "because it can be a divisive and emotionally charged topic".

Echoing an earlier statement, he insisted that he thought the hunt was legal and said he would assist authorities in Zimbabwe or the US in their inquiries.

Cecil, who was a major tourist attraction at Zimbabwe's largest game reserve in Hwange National Park, is believed to have died on 1 July, but the carcass was not discovered until a few days later.

How the internet descended on Walter Palmer

When is hunting not poaching?

Image copyright Paula French Image caption Experts say Cecil's six cubs are likely to be killed by the male lion who takes over the pride

Mr Palmer is said to have shot and injured the animal with a bow and arrow. The group did not find the wounded lion until 40 hours later, when he was shot dead with a gun.

The lion was later skinned and beheaded, according to the Zimbabwe Conservation Task Force (ZCTF), a local charity.

The animal had a GPS collar fitted for a research project by UK-based Oxford University that allowed authorities to track its movements. The hunters had tried to destroy it but failed, according to the ZCTF.

Mr Palmer's dental practice has closed its website and social media accounts since his identity was revealed after thousands of people flooded them with angry comments.

A protest was held outside the building on Wednesday.

About 100 protesters, both adults and children, stood around holding posters that had messages like "Justice for Cecil", "Trophy hunters are cowards" and "Prosecute poachers".

Two women from the Minneapolis-based Animals Rights Coalition said they organised the protest to raise awareness about animal cruelty.

Media playback is unsupported on your device Media caption Protesters are calling for Walter Palmer to be extradited to Zimbabwe to face charges

At the scene: Gary O'Donoghue, BBC News, Minneapolis

A man walks to the door of Walter Palmer's surgery and affixes a poster. It reads: "rot in hell".

A woman remonstrates with him. "That's completely inappropriate," she says, "he's still a human being". The man, unperturbed, refuses to take down the notice and the argument continues.

There are about 50 people hanging around outside Mr Palmer's surgery - which is closed - today's fillings going unfilled.

One protester brandishes a banner saying "let the hunter be the hunted" and a woman opines that he should hang for what he's done.

The police look on, no doubt bemused at the news crews and satellite trucks that occupy this suburban street in Minneapolis.

Earlier on Wednesday, professional hunter Theo Bronkhorst pleaded not guilty to a charge of "failing to prevent an unlawful hunt" at a court in Zimbabwe's capital Harare.

He was granted bail of $1,000 (£640) and ordered to appear in court again on 5 August. His co-accused - farm owner Honest Ndlovu - will appear at a later date.

The American tourist is believed to have paid about $50,000 (£32,000) to go on the hunt in Zimbabwe.

He is well known in the American hunting community. In 2006, he was found guilty of killing a black bear outside an authorised zone in the state of Wisconsin and lying to authorities about it. He was fined $3,000 (£1,900).

Mr Palmer has visited Zimbabwe for hunting trips in the past and one image posted online in 2010 shows him posing with a leopard he killed.

Media analysis - BBC Monitoring

Cecil's killing has attracted little media attention inside Africa.

What little comment there was came in the form of derisive editorials in Zimbabwean state media.

"Not since Simba, of The Lion King fame, has a lion captured the world's imagination in this way," Alex Magaisa wrote in the Zimbabwean Herald newspaper. While tragic, the lion's death has not inflamed local passions because it is "far removed from the lived realities of most of the local people", Magasia said, adding that tourism and hunting in Zimbabwe are "mired in elitism".

The writer said neither he nor his family had heard of Cecil the lion before it was killed.

Kennedy Mavhumashava struck a similar note in the Zimbabwe Chronicle and invoked the history of Western colonialism: "Many believe the lion was named after Cecil John Rhodes, the celebrated forerunner of British colonialism in Southern Africa, explaining the saturation coverage on the demise of his namesake."