A prominent critic of Russian President Vladimir Putin has been hospitalised with organ failure, two years after he almost died of suspected poisoning.

Journalist Vladimir Kara-Murza, who works for pro-democracy opposition group Open Russia, fell ill early on Thursday (02 February).

The journalist's wife told the BBC that he had the same symptoms as when he was previously seemingly poisoned.

"The ambulance took him directly to the hospital where the same medical team has since been trying to determine what is happening," she said.

"He was brought there conscious but put in a medicated coma and on life support later, because his organs began shutting down like last time," she told the BBC.

The night before, he shared a photograph on Facebook of a tribute to murdered Putin-opponent Boris Nemtsov.

Karza-Murza previously fell ill in May 2015, and was in critical condition for several days, before making a recovery.

He claimed he had been poisoned with a sophisticated toxin by political opponents.

The medical team that treated Kara-Murza in 2015 initially claimed that his illness may have been linked with the build-up in his system of a prescription anti-depressant, and a possible reaction to an allergy medication he had been taking.

Independent medical experts told RFE/RL that such severe symptoms are unlikely to have been triggered by the anti-depressant.

Karza-Murza divides his time between Washington DC and Moscow, and works for the organisation founded by prominent Putin opponent Mikhail Khodorokovsky. He has argued before the US Senate for sanctions to be imposed on Kremlin officials.