By Gabriela Baczynska and Maria Tsvetkova
MOSCOW (Reuters) - Russian opposition leader Alexei Navalny called on supporters to rally in protest on Monday against the results of a Moscow election which he says was rigged in favor of the Kremlin.
Results from Sunday's mayoral election showed Kremlin ally Sergei Sobyanin just cleared the 50 percent mark needed to win outright. Navalny challenged the outcome and demanded a run-off.
Buoyed by an unexpectedly strong showing of 27 percent which pushed him into second place, Navalny has raised the prospect of a new election stand-off in Russia, 19 months after allegations of fraud in a parliamentary election inspired the biggest protests against Putin since he rose to power in 2000.
"We call on all honest citizens who care about the city's fate to come along today to the officially sanctioned rally in Bolotnaya Square to support our demands and wait for the outcome of the negotiations," Navalny, 37, said in a statement.
He called for talks with the city authorities on the fraud allegations, which he said were backed up by election observers whose unofficial count put Sobyanin, appointed mayor by the Kremlin in 2010, just short of 50 percent.
"Yesterday we found out that we can win. Now we have to understand whether we can defend our victory," he said. "We made it into the second round but they again took it away from us."
Bolotnaya Square was the scene of the last big protest against Putin on May 6, 2012, the eve of his inauguration for a third term as president. Police broke it up after clashes with protesters and detained more than 400.
Opposition leaders portray that 2012 rally as the start of a crackdown on dissent to tighten Putin's grip on power, and regard Monday's rally as a chance to revive protests.
OPPOSITION STILL DIVIDED
Reigniting protests will not be easy. The opposition remains divided and opinion polls show Putin is Russia's most popular leader, with strong support outside the big cities.
Navalny also has a five-year jail term for theft hanging over him unless his appeal against the conviction succeeds. He says the sentence was Putin's revenge for challenging him and that it was intended to remove him as a political threat.
"It is a clear signal for the Kremlin that it must be seriously worried about Navalny," said Dmitry Oreshkin, a political analyst with sympathies for the opposition.
Navalny attracted votes beyond his core supporters, he said.
"But I am skeptical about the prospects of using this victory to mobilize the protest movement again on a mass scale."
Navalny's surge is still likely to cause consternation in the Kremlin.
Hardliners could portray his success as showing that the experiment in allowing an opposition leader to run has embarrassed the authorities.
Relative liberals may hail it as sign that establishment candidates can win an open race and push for greater openness in elections in the future.
Representatives from Putin's United Russia party, which dominates politics nationwide, still won most of the roughly 7,000 regional and local contests held across Russia on Sunday.
Official results in Moscow put Navalny on 27.24 percent but he said his real support was 35 percent. Sobyanin had 51.37 percent support in the city of nearly 12 million, a potential powerbase that can be used to amass influence and go on to bigger things in national politics.
Navalny promised to tackle corruption and took a tough line on immigrants in his campaign. Sobyanin used the roads, homes and offices built during his tenure to speak for him.
Navalny aides alleged Moscow authorities increased the vote for Sobyanin by adding people to voter lists at the last minute and manipulating mobile polling stations designed to let people confined to their homes vote. Election officials denied this.
"We have organized the cleanest, most competitive, most open election in the history of Moscow," Sobyanin, 55, told thousands of supporters around midnight.
He is a typical product of Putin's political system as a former leader of the oil-rich Tyumen region who went on to become head of the presidential administration in Moscow before being appointed mayor.
Navalny represents a new force. He built his reputation with an online campaign against corruption and with fiery rhetoric at protests and during his campaign.
Russian stock indexes rose on Monday, showing no sign of concern over the election. Foreign investors are likely to be worried by the election outcome only if a protracted standoff over the results leads to instability.
(Writing by Timothy Heritage; Editing by Angus MacSwan)