Opposition leader and former chess champion Garry Kasparov has dismissed this weekend's Russian elections as a farce.
He warns that Russians have been denied a choice in a campaign that has been dominated by Vladimir Putin's United Russia party.
Mr Kasparov spent five days in prison this week for taking part in an unauthorised protest against Mr Putin last weekend.
'The volume of falsification, violations and the volume of suppression of opponents, already makes the current regime illegitimate,' he told a news conference.
Sunday's elections are being closely watched for signs of Mr Putin's intentions after his second term in office ends next year.
Under the Russian constitution he cannot stand again in the presidential vote, set for 2 March.
However the ex-KGB officer, who came to power in 2000, has said that a strong victory for United Russia on Sunday will give him the moral mandate to continue playing a role in politics after he steps down as president in March.
Mr Putin and his Kremlin allies hope that a strong turnout at the polls and a convincing victory will give them a free hand to lay the groundwork for the presidential vote.
The campaign for the presidency kicked off on Wednesday with no frontrunner in sight and the clock is ticking for Mr Putin to tip his hand, as presidential candidates have until 23 December to register.
In the run-up to the elections, the Russian president accused his opponents of seeking to disrupt the elections and likened them to 'jackals' seeking funds from Western governments.
Opposition parties and non-governmental organisations have reported that millions of campaign leaflets have been confiscated during the campaign and that television coverage has been biased in favour of United Russia.
The Kremlin has denied the accusations and Mr Putin has pledged that the elections will meet democratic standards.
However, election watchdog organisations have voiced concern over allegations that voters have come under pressure from authorities to vote at their workplaces, under the watchful eye of their bosses.
And Europe's main election monitoring body, the Organisation for Security and Cooperation in Europe (OSCE), has decided to abandon its observer mission, citing restrictions from Moscow.
Mr Putin has accused the US, an OSCE member, of being behind the boycott and said it aimed to discredit Russia's elections.
Voting starts at 8pm GMT Irish time on Saturday in the far east region of Kamchatka and ends on Sunday at 6pm GMT in Kaliningrad, sandwiched between Poland and Lithuania.
