Thousands of supporters of Alexei Navalny took to the streets of Moscow Wednesday to protest his detention and back calls for the hunger-striking Kremlin critic to be given proper medical care.
Defying warnings and a huge police presence, the protesters in Moscow marched through the city centre near the Kremlin chanting "Freedom" and "Putin is a thief!", just hours after President Vladimir Putin delivered his annual state of the nation address.
Though large crowds gathered, the protests were not on the scale of pro-Navalny demonstrations seen earlier this year, when tens of thousands rallied and thousands were arrested.
Police said 6,000 people had gathered in Moscow.
"This is a fight for the future, we don't have any here," 51-year-old protester Andrei Zamyatin told AFP in central Moscow.
"Navalny is trying to change the system and is being punished for it."
In Russia's second city Saint Petersburg some 4,500 protesters gathered, police said.
A few hours after the demonstration began, an AFP journalist in Saint Petersburg saw security forces move in to forcefully detain the protesters, with at least one man hit with a taser and police chasing people into subway stations.
Demonstrations earlier took place in other large cities including Vladivostok in the Far East, and Novosibirsk, Irkutsk and Tomsk in Siberia, with police saying more than 14,000 people had protested in 29 cities.
Police had issued a warning against taking part in "illegal gatherings" and detained more than 450 people across the country, according to monitoring group OVD-Info.
Among those detained in Moscow were Navalny ally Lyubov Sobol and his spokeswoman Kira Yarmysh.
The protesters are demanding that Navalny, who launched a hunger strike three weeks ago, be freed or at least given proper medical treatment after his doctors said his health was failing and he could die "at any minute".
Those taking part said they believed it was important to join the demonstrations, but few expected the Kremlin to listen.
"I don't think this protest can save Navalny. There would need to be at least 200,000 to 300,000 people in the streets," said protester Alexander Butuzov, 51.
Navalny was arrested when he returned to Russia in January after months recovering in Germany from a near-fatal nerve agent poisoning he blames on the Kremlin -- an accusation it rejects.
He was sentenced to two-and-a-half years on old fraud charges his supporters say were politically motivated and has been serving time in a penal colony about 100 kilometres (60 miles) east of Moscow.
His health has been failing since he launched his hunger strike to demand proper medical care for a range of ailments.