Former head of Rwanda's presidential guard Tom Byabagamba, 59, who once served as President Paul Kagame's personal bodyguard, has died in jail.

He was arrested in 2014 along with his brother-in-law Frank Rusagara, a retired brigadier-general, for "spreading rumours" and "tarnishing the image of the country and government".

Right groups expressed concern over their cases, framing them as a part of a pattern of government repression. Throughout his trial, Col Byabagamba denied the allegations against him, saying they were fabricated.

Byabagamba's brother David Himbara told the BBC Great Lakes service his family did not know the cause of death as "no-one was allowed to see him in all these years".

Rights groups have repeatedly accused Kagame's government of restricting political opposition and silencing critics within Rwanda and abroad.

In 2016, a military court convicted Byagamba and imprisoned him for 21 years, although this was later reduced to 15 years on appeal. Rusagara, who had also been secretary-general of the defence ministry, was given a 20-year sentence.

Rusagara died in prison in March last year. At the time Human Rights Watch (HRW) described it as the "lonely death of a general", noting that his family had not heard his voice since 2014, days before his arrest.

His family was informed by the authorities that Rusagara had been ill with cancer, the rights group said.

The conviction of the two men had followed a "flawed trial" marked by "serious allegations of torture and witness tampering", according to HRW.

Campaign group Freedom Now had also previously criticised their detention as "arbitrary" and as having "violated international law".

Byabagamba leaves behind two sons and a wife.