Image copyright Reuters Image caption Prince was found dead at his Minneapolis-area estate on 21 April

US singer Prince died from an accidental overdose of the painkiller fentanyl, medical examiners have found.

The report, from the Midwest Medical Examiner's Office in Minnesota, comes more than a month after the singer was found slumped in a lift at his home.

Detectives have already questioned a doctor who saw the 57-year-old twice in the weeks before he died.

Prescription painkillers were in the singer's possession following his death, officials told US media in May.

A police warrant has also revealed that Dr Michael Schulenberg prescribed medication to the singer on 20 April - the day before he died.

The warrant does not say what was prescribed or whether Prince took the drugs.

According to the autopsy report, Prince self-administered fentanyl, an opioid many times more powerful than heroin.

In March last year, the US Drug and Enforcement Administration warned the drug, which it said was often laced in heroin, was a "threat to health and public safety".

It said even small doses of fentanyl could be lethal and that "incidents" and overdoses related to the drug were "occurring at an alarming rate".

Prince was found unresponsive in a lift at his Paisley Park Studios on the morning of 21 April, local officials said. First responders tried to revive him with CPR but he was pronounced dead shortly afterwards.

He is believed to have suffered from knee and hip pain from years of performing, the Associated Press news agency reports, citing a friend.

Artists from around the world and Prince's numerous fans later paid tributes to the star.

Image copyright AFP Image caption Prince's sudden death shocked people around the world

Prince was cremated in a private ceremony on 24 April. The singer's family are understood to be planning to stage a public memorial in August.

He was a prolific writer and performer from a young age, reportedly writing his first song when he was seven.

A singer, songwriter, arranger and multi-instrumentalist, Prince recorded more than 30 albums. His best known hits include Let's Go Crazy and When Doves Cry.

What is fentanyl?

Fentanyl is an extremely strong painkiller, prescribed for severe chronic pain, or breakthrough pain which doesn't respond to regular painkillers.

It is an opioid painkiller which means it works by mimicking the body's natural painkillers, called endorphins, which block pain messages to the brain.

It can cause dangerous side effects, including severe breathing problems.

The risk of harm is higher if the wrong dose or strength is used.