A former Rwandan minister, Jacques Bihozagara, who was jailed in Burundi for spying has died.
His death comes nearly four months after he was arrested.
No official reason has been given for the death of the Rwandan ambassador to Belgium.
Rwanda which has expressed ‘shock’ at the news is demanding answers from Burundi.
Relations between the two neighbouring countries have been strained recently, amid claims that Rwanda was backing rebels seeking to overthrow Burundi’s president, Pierre Nkurunziza, a claim Rwanda has denied.
A Burundian justice ministry spokesman is quoted by the BBC as saying Bihozagara ‘fainted and died in the afternoon’‘.
He died within minutes of arriving at the prison hospital, according to fellow prisoners.
A Rwandan foreign ministry official told AFP news agency that he had been illegally detained and urged the authorities to clarify his sudden death, “which raises many questions”.
Bihozagara, a former youth minister in Rwanda as well as a former ambassador to Belgium and France according to AFP, was arrested on December 4, 2015 by Burundi’s National Intelligence Service (SNR), an agency under the direct control of President Nkurunziza.
According to Rwanda’s New Times newspaper, the former diplomat lived in Burundi before the 1994 genocide in Rwandan and since he retired, he visited Burundi regularly for business.