Alexei Navalny, the Russian opposition leader and Kremlin critic, was doused with green dye as he campaigned in Siberia on Monday.
An unknown assailant splashed a green antiseptic liquid in Mr Navalny’s face during a campaign stop in the city of Barnaul, about 1800 miles east of Moscow.
A video filmed by the anti-corruption campaigner’s supporters shows a man approaching Mr Navalny as he walks along a street before flinging the liquid, known in Russian as “zelyonka,” in his face. The attacker, in a black coat, then flees.
“It burnt a lot, and I had a horrible thought that it was acid,” Mr Navalny said in a blog post shortly after the incident.
To his relief, he joked, he has been left unharmed but looking like “either Avatar, or the Mask, or Shrek.”
“This is a strange presumption on the Kremlin's part: if they pour zelyonka over me, I will stop campaigning and organising rallies," he added. “Maybe they thought I would stop recording video’s with a green face. But I’ll do more, because more people will watch,” he said in a video statement.
Zelyonka, a dilute alcoholic solution of the triarylmethane dye Brilliant Green, is sold in Russian pharmacies as a topical antiseptic.
While not harmful in contact with the skin, its vivid green colour is notoriously hard to wash off.
The images of Mr Navalny addressing a rally with a bright green face drew a humorous response from Twitter users, with some of his supporters dousing themselves in the liquid and post pictures of themselves with green faces in response.
Victoria Navalny, Mr Navalny’s sister-in-law and wife of his imprisoned brother Oleg, posed with her son with a green face in solidarity.
Nikolai Danilov, a journalist, was reportedly arrested by Moscow police for showing up on Red Square with a green face.
Mr Navalny led a series of anti-government demonstrations in Moscow in 2011 and 2012, and is known for publishing embarrassing investigations into the personal fortunes of top Kremlin officials.
He is touring Russia ahead of the 2018 presidential election, in which he intends to challenge Vladimir Putin, the incumbent, for the keys to the Kremlin. He was in Barnaul to open a local campaign headquarters.