OVD-Info, which monitors detentions at opposition protests, said that by around 2:20 pm Moscow time (1120 GMT) on Sunday, 1,103 people had been detained across 35 cities.
The highest numbers held were in the Siberian city of Novosibirsk and in Yekaterinburg in the Urals.
Riot police also detained protesters who gathered on squares in the country’s largest cities of Moscow and Saint Petersburg.
Memorial, Russia’s most prominent rights group, said that one of its leading activists, Oleg Orlov, was detained on Moscow’s Manezhnaya Ploshchad square as he held a placard.
Russian police on Friday had warned that all attempts to hold illegal demonstrations on Sunday would be “immediately suppressed” and organisers and participants would face charges.
The latest detentions brought the total number of demonstrators held to almost 10,000 since February 24, when President Vladimir Putin ordered troops into Ukraine to carry out a “special operation”.
Despite the official crackdown on demonstrations, and protesters facing jail terms, there have been daily protests since then.
Earlier this week, jailed Kremlin critic Alexei Navalny urged Russians to stage daily demonstrations, saying the country should not be a “nation of frightened cowards”.
Putin on Friday signed into law a bill introducing jail terms of up to 15 years for publishing “fake news” about the Russian army.
With inputs from NDTV
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