Dozens of anti-war demonstrators were detained in Moscow and Saint Petersburg Wednesday after jailed Kremlin critic Alexei Navalny called on Russians to protest President Vladimir Putin's invasion of Ukraine.

Police in Putin's hometown of Saint Petersburg violently dispersed protesters and detained around 100 people, an AFP journalist at the scene said.

In Moscow, law enforcement closed off Red Square near the Kremlin and detained at least seven people who gathered while loudspeakers warned people from convening.

The demonstrations Wednesday came hours after Navalny called for daily rallies against the military assault, saying Russia should not be a "nation of frightened cowards" and calling Putin "an insane little tsar".

In Moscow, one woman in a red coat shouted "No war!" before being hauled off by police to a van, according to an AFP journalist.

Police officers detain a woman during a protest against Russia's invasion of Ukraine in Saint Petersburg
Police officers detain a woman during a protest against Russia's invasion of Ukraine in Saint Petersburg AFP / Olga MALTSEVA

"It pains me to see what is happening and to do nothing," a man in his fifties told AFP, before being arrested with his son, 17.

"I couldn't stay at home. This war has to be stopped," student Anton Kislov, 21, told AFP in Saint Petersburg.

Independent monitoring group OVD-Info said that more than 7,000 people in total in Russia had been detained at demonstrations over Moscow's invasion of Ukraine that began last Thursday.

Navalny, 45, led the biggest protests in Russia against Putin in recent years and was targeted in a poisoning attack he blames on the Kremlin in 2020.

He is now serving a prison sentence on old fraud charges outside Moscow.