A video purportedly showing popular Cameroonian singer Simon Longkana Agno, widely known as Longue Longue, being tortured has led to widespread outrage in the country.

The artist, renowned for making hits about bad governance, colonialism and other social ills, said the video was taken after he was arrested in 2019, but this is the first time it has been seen by the public.

Longue Longue shared it himself. He told the BBC he had got the video from an unknown source in America, who had sent it to him.

The Cameroonian authorities said in a statement they had opened an investigation into the "unfortunate incident".

Warning: This article contains a picture and descriptions of torture

In the video, Longue Longue's hands are cuffed behind his back, and he is sitting on the floor in his underwear as the soles of his bare feet are beaten with a flat machete.

Despite his desperate pleas for the beating to stop, the men, alleged by Longue Longue to be security agents, continue.

The BBC has been unable to verify the video.

On his Facebook page, he said he was arrested for his "freedom of thought", and promised to file legal complaints in both Cameroon and France, where he is now living.

"It's been three months since I left Cameroon, I didn't feel safe there any more," the 51-year-old artist told BBC Afrique.

Longue Longue added that he didn't want to be in the country for the presidential election due next year.

He said he felt safer in France but was still worried about his family back home.

The singer said he had received threats after announcing he was going to publish the video.

"I received calls saying that if it ever gets made public, they will go after my family," he explained.

He was arrested in 2019 after posting a video saying that long-time President Paul Biya had rigged the 2018 election.

The artist said opposition leader, Maurice Kamto of the Cameroon Renaissance Movement (CRM), was the rightful winner of the polls.

At the time, the Constitutional Council rejected Kamto's demand for a re-run because of alleged rigging.

The opposition leader is among those to have denounced the apparent torture and called for an investigation into the incident.

"The CRM strongly condemns this state barbarity and demands the urgent opening of an enquiry to arrest and immediately bring before the courts the perpetrators of these inhuman acts," Kamto said in a statement on X.

He added that the video was "reminiscent of the horrific treatment" opposition activists faced during the crackdown in 2019 when hundreds of his supporters were detained.

Renowned Cameroonian human rights lawyer Akere Muna said Longue Longue's treatment was a "stark reminder of the depths of depravity to which humanity can descend".

Rights groups have criticised the government for creating an atmosphere of impunity for members of the country’s security forces.

They have also accused the authorities of cracking down on dissent ahead of next year’s presidential election.