Russian opposition leader figure Alexei Navalny says he was splashed with a bright green dye on Monday by an unknown assailant as he attended the opening of an office for his campaign against president Vladimir Putin.

Mr Navalny said the assailant shook his hand, then splashed him with the dye before escaping in a car that drove off to the local government offices in the Siberian city of Barnaul. Several opposition activists have been attacked in similar circumstances while attempting to run for office or organize protests against Mr Putin.

Mr Navalny, an anti-corruption lawyer, is attempting to run for president next year despite being barred from the ballot over a recent fraud conviction. After the European Court of Human Rights overturned an earlier conviction in the same case last year, the same court hurriedly held the trial again and gave him the same suspended felony sentence word-for-word in February.

Mr Putin, who has ruled Russia almost unchallenged since 2000, is expected to announce his bid for a new six-year term.