(CNN) With cries of "Putin out" and "Russia without thieves," mass protests took place in cities across Russia on Monday -- a day that was supposed to celebrate the nation.

The national day was picked by opposition leader Alexey Navalny for the latest round of rallies designed to muster support for his bid to unseat President Vladimir Putin at next year's election.

Why now?

The 41-year-old activist has been an outspoken critic of what he says is a corrupt regime led by Putin and his allies -- in particular Prime Minister Dmitry Medvedev -- and is using allegations of government impropriety to muster support.

Navalny is hoping the scale of the protests will match the turnout of demonstrations in March, when thousands took to the streets across Russia.

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