The green liquid used in the attack is a common Russian antiseptic, which remains on the skin for days
Russian opposition leader Alexei Navalny has turned green after an unknown assailant sprayed a liquid onto his face in the street.
The attack reportedly happened as the leading Kremlin critic and anti-corruption campaigner stopped to shake a man's hand in the Siberian city of Barnaul.
The green liquid used in the attack is a common Russian antiseptic, which remains on skin for days but is otherwise harmless.
Mr Navalny appeared to take the attack in his stride, tweeting: "I will be opening a headquarters in Barnaul as if I'm from the film The Mask! Cool. Even my teeth are green!"
The tweet was a reference to the Hollywood film, The Mask, in which Jim Carrey played a superhero who wore a green mask.
The anti-Putin campaigner was in Barnaul to open his headquarters in the city as part of his campaign to stand in Russia's 2018 presidential elections.
He is currently unable to stand for election due to a criminal conviction for fraud, but his supporters say the charges against him are politically motivated.
Mr Navalny rose to prominence in Russia during the protests against Vladimir Putin's return as president in 2012.
Earlier this month he accused Russia's Prime Minister Dmitry Medvedev of large-scale corruption, which was dismissed as electioneering by the Moscow regime.
Additional reporting from IRN