"We're just trying to make people understand that you have to fight for your rights and they're rounding people up with mass arrests," Valery Smirnov, a 23-old-year construction engineer, said at the Moscow rally.

The prosecutor's office for central Moscow had warned that Navalny and any other participants would "face the consequences under the law of the Russian Federation."

In Moscow's Pushkin Square, thousands of protesters mingled with hundreds of Putin supporters chanting "Russia, Russia" and wearing ribbons associated with the May 9 Victory Day celebration, a holiday on which tanks and troops parade on Red Square in a display of Russian military might to commemorate the end of World War II.

Protesters chanted "Putin is a thief" and other anti-government slogans. Later, with a police helicopter flying overhead that drowned out the sound of the demonstrators, phalanxes of officers moved through the crowd forcing them to disperse or face arrest.

Protesters said they weren't intimidated by the use of force. "I'm here because it's important to voice my views," said Angelina Karpenko, 25, who works in an architect's office. "We deserve better."

Saturday's unrest came less than a week after tens of thousands protested on May 1 against restrictions on the internet after the authorities started trying to block the popular Telegram messaging messaging app. Navalny addressed that rally in Moscow.

Putin faces mounting challenges as stagnant growth steadily eats away at living standards and the government braces for unpopular belt-tightening measures such as increasing the pension age. He's also locked in a standoff with the West that's provoked increasingly painful sanctions and must decide how to settle the issue of succession when his final term allowed under the Constitution ends in 2024.

Navalny, who was barred from challenging Putin in the presidential vote, has lost momentum since last year, when he staged the biggest protests since those provoked by alleged ballot-rigging in 2011-2012.

The 41-year-old opposition leader and anti-corruption activist, who almost managed to force a run-off against a Putin ally in Moscow's mayoral elections in 2013, is counting on an upsurge in social discontent to erode support for Putin and the ruling system in the years ahead.

"Navalny is very far-sighted, he is waiting patiently for the opportunity to exploit popular dissatisfaction," said Alexei Makarkin, an analyst at the Moscow-based Centre for Political Technologies.

Bloomberg