Open this photo in gallery Rwandan gospel singer Kizito Mihigo, centre, is seen in 2018 being released from the Nyarugenge prison. CYRIL NDEGEYA/AFP/Getty Images

One of Rwanda’s most famous musicians has been found dead in police custody, the latest in a long list of dissidents to die under mysterious circumstances after tangling with Rwandan President Paul Kagame.

Kizito Mihigo, a popular gospel singer and genocide survivor who helped compose Rwanda’s national anthem, was found dead Monday in a police cell in the capital, Kigali.

He was arrested last week for allegedly trying to cross the border illegally into Burundi and was accused of trying to bribe the police and seeking to join “terrorist groups” there.

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Rwandan police, in a statement quoted by semi-official Rwandan media, said the 38-year-old musician “used bedsheets to strangle himself to death.”

But on social media, many opponents of the Rwandan government voiced skepticism about the official version, saying the musician was killed by the police.

Human-rights activists are calling for a full investigation. There are growing concerns about human-rights abuses in Rwanda as it prepares to host the Commonwealth Heads of Government Meeting in June, which is expected to be attended by Prime Minister Justin Trudeau and dozens of other world leaders.

Mr. Mihigo had been a cultural icon in Rwanda – a hugely popular celebrity and peace activist who often sang the national anthem at state functions. But he ran into trouble with the authorities in 2014 when he released a song that questioned the official version of the country’s 1994 genocide, in which an estimated 800,000 Rwandans died.

The song called for Rwandans to remember all the victims, including those who were “slaughtered in revenge” – an implicit reference to the victims of Mr. Kagame’s army, which killed thousands of people in the mid-1990s as he seized control of the country after the genocide.

The song was immediately banned, and Mr. Mihigo was arrested a few days later. He was sentenced to 10 years in prison for treason and conspiring to “murder or harm” Rwandan government leaders. He was released from prison in 2018 when Mr. Kagame gave clemency to more than 2,000 prisoners.

A police statement Monday said Mr. Mihigo had been in a police cell for three days when he was found dead.

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“Kizito Mihigo’s death in custody raises serious questions that need a prompt and thorough investigation by the authorities,” said Lewis Mudge, Central Africa director at Human Rights Watch, in a statement Monday.

“Too often, sensitive cases in Rwanda result in mysterious deaths or disappearances,” he said. “The investigation should examine the possibility that Mihigo could have been ill-treated or killed in custody.”

Amnesty International said it was “shocked and deeply saddened” by the news of Mr. Mihigo’s death. The Rwandan authorities “must immediately launch an independent, impartial and thorough investigation to determine the cause of death – including whether it was natural or accidental, or a case of suicide or homicide,” Amnesty said in a statement Monday evening.

Filip Reyntjens, a Belgian scholar and leading expert on Rwanda, said the diplomatic community in Kigali “must request an independent inquiry and post-mortem” into Mr. Mihigo’s death.

The Commonwealth summit is scheduled to be held in Kigali on June 26-27, with all 53 Commonwealth countries expected to be represented. Democracy and the rule of law are among the summit’s official themes.

Mr. Trudeau has often met with Mr. Kagame, most recently on Feb. 8 at the African Union summit in Addis Ababa, where they “exchanged views on priorities for the upcoming Commonwealth Heads of Government Meeting,” according to a statement from Mr. Trudeau’s office.

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Last September, a senior official of a Rwandan opposition party, the FDU-Inkingi party, was stabbed to death by unidentified attackers. At least six of the party’s members have died or disappeared without a trace over the past three years, while nine others have been jailed on terrorism allegations. Amnesty International said the killings and disappearances are alarming and suspicious.

There is also evidence the Rwandan government has sent death squads on missions to kill dissidents abroad. Last September, a South African judge issued arrest warrants for two Rwandans with alleged links to the Kagame government, accusing them of involvement in the strangulation death of prominent Rwandan dissident Patrick Karegeya in a Johannesburg hotel room.

Last month, a report by Human Rights Watch documented how street children in Kigali are routinely rounded up and beaten at an official detention centre, where they are kept in degrading and overcrowded conditions.

In a report this month, the United Nations Committee on the Rights of the Child called on Rwanda to take “urgent measures” to end the abuse of street children and to halt their arbitrary detention.