"We will do everything so that Sergei Sobyanin's victory will cost him dearer than any defeat," Navalny said after coming second to the Kremlin-backed incumbent in Sunday polls for Moscow mayor.
"We now have documentary and legal evidence that a second round should have taken place and that the Moscow election commission falsified the poll," the 37-year-old said on popular Moscow Ekho radio.
The Moscow election commission today upheld the final result, saying that Sobyanin received 51.3 per cent of ballots, just barely enough to avoid a run-off.
In a blog post, Navalny said Sobyanin avoided a second round runoff with a margin of just 31,000 votes, accusing the winner of manipulations at the ballot box.
More From This Section
An anti-corruption blogger, Navalny shot to prominence during huge anti-Putin rallies in the winter of 2011-12.
Analysts said Navalny's stronger-than-expected showing propelled him to celebrity status in Russian politics and made him a force to be reckoned with.
The turnout stood at a meagre 32 per cent which apparently reflected Muscovites' apathy and lack of conviction that they can effect change.
But in a sign that the Moscow authorities were in no mood to hold a vote recount, the city's election commission upheld the final results today.
Independent vote monitors have said irregularities were registered in Sunday's election, although they were not as serious as those witnessed in previous polls.
Putin was scheduled to attend the Moscow mayor's inauguration on Thursday, a Kremlin source said last week.
Navalny said the authorities were in a hurry to hold the inauguration as soon as possible to cement Sobyanin's win.
"They understand perfectly well that we have thousands of observers from whom we need to collect papers in order to prepare thousands of complaints," he said.