Russian authorities accuse him of exaggerating his medical condition to grab attention, and of refusing prison medical care.

They have pledged to ensure he survives.

Navalny travelled to Germany last August for treatment after being poisoned by a nerve agent in an attack he blamed on Putin.

The Kremlin has said it has seen no evidence he was poisoned and has denied any Russian role if he was.

He was arrested in January when he returned to Russia and jailed for two-and-a-half years in February for parole violations he said were fabricated.