The pro-Kremlin mayor of Moscow was Sunday set to win re-election in the Russian capital despite an unexpectedly strong challenge from a top critic of President Vladimir Putin, exit polls said.
Sergei Sobyanin, a leading ally of Putin, would win the elections in the first round with just over half the vote, with anti-Kremlin critic Alexei Navalny picking up around a third of the votes, two Kremlin-linked polling agencies said.
But Navalny's campaign headquarters immediately cast doubt on the exit polls and said he had managed to force a second round, raising the prospect of tense days ahead if the exit polls are confirmed by official results.
The candidacy of anti-corruption crusader and protest leader Navalny has made the race the first genuinely competitive Russian election since the heady early post-Soviet years.
Addressing cheering supporters at his election headquarters after Moscow's first mayoral polls in a decade, Navalny, 37, accused Putin and Sobyanin of concocting a figure that suited them.
"Right now Sobyanin and his main supporter Vladimir Putin are deciding whether to have a relatively honest election and to have a second round, or not," he said, appearing pleased with his result.
He warned the city authorities against rigging the vote. "We will demand a run-off," he told popular radio Moscow Echo, saying his campaign was waiting to hear from observers.
The vote was seen as a crucial test of the protest mood in the city which was shaken by huge demonstrations against Putin's decade-long rule in the winter of 2011-2012.
Sobyanin was due to retain the post of mayor in the first round with 52.5 percent of the vote while Navalny is due to get 29.1 percent, the Kremlin-connected FOM polling group said after polls closed at 1600 GMT.
A second exit poll by the VTsIOM, another Kremlin-linked polling agency, gave a similar projection, putting Sobyanin on 53 percent and Navalny on 32 percent.
"This is a victory for Navalny, the results he's received are very good, even if there will be no run-off," Gleb Pavlovsky, a political analyst and one-time Kremlin consultant, told AFP.
Navalny's campaign insisted its polls showed Sobyanin had won only 46 percent, meaning their candidate had forced a second round with 35.6 percent of the vote.
Turnout stood at 26.5 percent as of 1400 GMT, an unusually slack figure compared to recent high-profile polls. Communist candidate Ivan Melnikov was predicted to come third.
--- 'What will they do with Navalny now?' ---
Putin, who has made no secret of his support for his former Kremlin chief of staff Sobyanin, 55, said Moscow did not need a "politician" for a mayor when he cast his vote.
Moscow gave Putin a relatively low 46.95 percent of the vote in the 2012 presidential election, well below the nationwide average.
Navalny has threatened protests if officials rig the vote and thousands of supporters are due to hold a meeting on Monday evening in a central Moscow square to decide their strategy.
He shot to prominence during the anti-Putin rallies, earning comparisons to a young Boris Yeltsin, Russia's first post-Soviet president, for his exuberant energy, good looks and promise of change.
"He embodies the fight against corruption, honesty, protest against the regime," said Ivan Volkov, 28, after casting his ballot.
Many said they were voting for Sobyanin because he had done a lot for Moscow since his appointment to the post in 2010.
"With his arrival Moscow has become better," said Yevgenia Zatsepina, 78. "He is someone who keeps his promises."
Throughout the campaign the buttoned-up Kremlin functionary avoided overt political rhetoric and shunned television debates, instead focusing on sprucing up the capital of 12 million.
By contrast, Navalny made headlines with a Western-style political campaign securing more than 100 million rubles ($3 million/2.3 million euros) in donations.
In July, Navalny was sentenced to five years in a penal colony on fraud charges that he says were trumped up and arrested in court. A day later he was suddenly released pending his appeal.
"The question is, what will they do to Navalny now," said Nikolai Petrov, an analyst with the Higher School of Economics.
"I think his term will be commuted to a suspended sentence -- this will prevent protests from flaring up and will also exclude him from politics for some time."
The Moscow election was part of a nationwide day of local polls, with Kremlin-backed establishment figures also being challenged in key cities like the main Urals centre of Yekaterinburg.
In Yekaterinburg, the ruling party candidate Yakov Silin was running in a tense battle against anti-drugs campaigner and opposition activist Yevgeny Roizman, who stands a real chance of winning the post of city mayor.