More than 559 people were detained at protests on Sunday in 21 cities across Russia against President Vladimir Putin's invasion of Ukraine, according to an independent Russian-based protest monitor.

The OVD-Info protest monitoring group said people were detained at protests including in the Russian Pacific port city of Vladivostok and the Siberian city of Irkutsk. Opposition activists posted videos showing protests in other cities.

Reuters was not able to independently verify the information. Reuters was unable to reach spokespeople for the police in Vladivostok or Irkutsk. Russia's interior ministry could not be reached for comment. The interior ministry warned on Saturday that any attempt to hold unauthorised protests would be prevented and the organisers held to account.

A video posted on social media showed a protester on a square in the far eastern city of Khabarovsk shouting: "No to war - how are you not ashamed" before two policemen detained him. Police used loudspeakers to tell a small group of protesters in Khabarovsk: "Respected citizens, you are taking part in an unsanctioned public event. We demand you disperse."

Reuters was not able to independently verify the post. Jailed Kremlin critic Alexei Navalny had called for protests on Sunday across Russia and the rest of the world against the invasion launched by Russia on Feb. 24.

About 2,000 people attended an anti-war protest in Kazakhstan's biggest city Almaty, videos posted on social media showed. Reuters was unable to independently verify the posts. The crowd shouted slogans such as "No to war" and "Putin is a dickhead", while waving Ukrainian flags.

Activists put blue and yellow balloons in the hand of a Lenin statue towering over the small square where the rally took place. "Because of Putin, Russia now means war for many people," Navalny said on Friday. "That is not right: it was Putin and not Russia that attacked Ukraine."

Putin, Russia's paramount leader since 1999, ordered what he casts as a special military operation to defend Russian-speaking communities against persecution in Ukraine and to prevent the United States from using Ukraine to threaten Russia.

The West has called his arguments a baseless pretext for war and imposed sanctions that aim to cripple the Russian economy. The United States, Britain and some other NATO members have supplied arms to Ukraine. Putin's approval ratings have jumped in Russia since the invasion, according to Moscow-based pollsters.

Putin's rating rose 6 percentage points to 70% in the week to Feb. 27, according to state pollster VsTIOM. The FOM pollster, which provides research for the Kremlin, said Putin's rating had risen 7 percentage points to 71% in the same week.