Russian opposition leader Alexei Navalny has been barred from running in next year's presidential election after officials ruled he was ineligible to take part due to a suspended prison sentence he says was trumped up.
The decision by the central election commission on Monday was widely expected as election officials had repeatedly declared Navalny would be ineligible to run.
Twelve members of the 13-member commission voted to bar Mr Navalny. One member abstained, citing a possible conflict of interest.
Mr Navalny, 41, who polls show would struggle to beat incumbent Vladimir Putin in the March election, said he would appeal and called on his supporters to boycott the election and campaign against it being held.
"We knew this could happen, and so we have a straight-forward, clear plan," Mr Navalny said in a pre-recorded video released immediately after the decision.
"We announce a boycott of the election. The process in which we are called to participate is not a real election. It will feature only Putin and the candidates which he has personally selected."
Mr Navalny said he would use his campaign headquarters across Russia to support the boycott and monitor turnout on voting day, March 18.
Polls show Mr Putin, 65, who has dominated Russia's political landscape for the last 17 years, is on course to be comfortably re-elected, making him eligible to serve another six years until 2024, when he turns 72.
Allies laud Mr Putin as a father-of-the-nation figure who has restored national pride and expanded Moscow's global clout with interventions in Syria and Ukraine.
Mr Navalny says Mr Putin's support is exaggerated and artificially maintained by a biased state media and an unfair system. He says he could defeat him in a fair election, an assertion Mr Putin's supporters have said is laughable.
There had been some speculation prior to the decision among the opposition that Mr Navalny might be allowed to run in order to inject more interest into what looks like a predictable contest amid Kremlin fears that apathetic voters might not bother to vote.
Mr Navalny has been jailed three times this year and charged with breaking the law by repeatedly organising public meetings and rallies.