Russian presidential spokesperson Dmitri Peskov said that the Federal Penitentiary Service was investigating following the announcement of the death of opposition leader Alexei Navalny in a penal colony on Friday.

"As far as we know, now, in accordance with all existing rules, the Federal Penitentiary Service is engaged in all inspections, enquiries and so on," he said. "In other words, it does not require any instructions, because there is a certain set of rules for such a case, which are now being followed by the Federal Penitentiary Service."

Asked to comment on reports about cause of death - potentially a 'thrombus detachment' or blood clot - Peskov replied that he didn't know and that the 'medics have to find this out'.

Navalny's death was reported by Russia's Federal Penitentiary Service on Friday. He was 47.

The opposition leader returned to Moscow in January 2021, after being treated in Germany for an alleged poisoning attempt while on a flight in Russia in August 2020.

Navalny was initially detained at the airport in the Russian capital, and sentenced to two and a half years in jail for a parole violation stemming from a 2014 embezzlement conviction.

He was subsequently charged with fraud and contempt of court, and given another nine years in prison. Navalny claimed all accusations against him were politically motivated.

In August 2023 he received a further 19 years for inciting and financing extremism, among other charges.