Three 16-year-old girls brought sheets of paper to the Moscow protest and sat on the pavement to write the articles of the Russian Constitution on them; a nearby group of teenagers climbed atop of a tent with posters saying, "Corruption kills the future".
With cries of "Putin out" and "Russia without thieves", mass protests took place in cities across Russian Federation on Monday - a day that was supposed to celebrate the nation.
The Moscow protest is due to run from 1100 to 1400 GMT.
Navalny was detained outside his home an hour before the rally was to start.
The protesters, some carrying Russian flags, were chanting loudly as Moscow riot police stood watch.
"The United States strongly condemns the detention of hundreds of peaceful protesters throughout Russia", Spicer said, calling it "an affront to core democratic values".
People are demonstrating against alleged fraud in the Russian government. Navalny says the charges against him are politically motivated.
"I am glad that the protest movement is getting younger", Yashin said in a posting that showed a young woman next to riot police late Monday.
Demonstrators in Monday's opposition protests across Russian Federation say they are fed up with endemic corruption among officials.
Navalny has become the most prominent figure in an opposition that has been troubled by factional disputes.
The demonstrators appeared to skew predominantly younger - those who were born or grew up during Vladimir Putin's 17 years of leading Russian Federation. Similar crowds turned out in March, rattling officials who had perceived the younger generation as largely apolitical.
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The protests in March took place in scores of cities across the country, the largest show of discontent in years and a challenge to President Vladimir Putin's dominance of the country.
Navalny was among those arrested Monday.
Instead, he urged demonstrators to gather on Tverskaya Street, a main Moscow avenue that was closed to traffic for a celebration of the national Russia Day holiday that included people dressed up in various costumes from the country's history.
In the photo, a rally in the city of Vladivostok, where according to the data of the OVD-info, 11 people were detained.
In St. Petersburg, an Associated Press reporter counted about 500 people forced into police buses. Police in St Petersburg arrested about 50 protesters at the unsanctioned protest at Mars Field.
Navalny's wife, Yulia, reported news of his detention at his home in Moscow on his official Twitter feed. Prior to his arrest, Navalny claimed authorities had pressured companies to refusing to supply audio and video equipment to humiliate the protesters.
Navalny's Fund for Fighting Corruption had been providing updates on protests throughout the country Monday. Authorities have said the protest is illegal. During a March 2017 protest that was organized by Navalny, over 1,000 were arrested.
Navalny said contractors hired to build a stage at the agreed-upon venue couldn't do their work.
Authorities in Moscow had authorised a venue for the protest away from the city centre.
"Any provocative actions by the protesters will be viewed as threat to public order and immediately thwarted", the police said.