Thousands of supporters of jailed Russian opposition leader Alexei Navalny took to the streets of Moscow to protest his detention and back calls for his immediate and proper medical care, The BBC reported Thursday.

Authorities arrested more than 1,000 protesters Wednesday as Russians in several cities joined rallies organized by allies of the hunger-striking Putin critic over his deteriorating health behind bars.

The last time such protests took place, in January and February this year after Navalny's arrest, massive crowds turned out and more than 11,000 were rounded up and detained, according to independent rights watchdogs.

Defying warnings and an imposing police presence, the demonstrators in Moscow marched through the Kremlin shouting "Putin is a thief!" and "Freedom" moments after Russian President Vladimir Putin delivered his annual state of the nation address.

The demonstrations fell short of the half million protesters that Navalny's team had expected to draw, but major crowds in St. Petersburg, Moscow and other cities have shown the resilience and dedication of his supporters.

"This is one of the last gasps of a free Russia, as many are saying. We came out for Alexei... against a war in Ukraine and the wild propaganda," Reuters quoted Marina, a student who participated in the Moscow protest, as saying.

The Kremlin has intensified its crackdown in the months since February, targeting Navalny's associates, independent members of the media and human rights groups. Wednesday's protests, although smaller, were a show of anger and defiance.

"This is a fight for the future, we don't have any here," Andrei Zamyatin, 51, told AFP. "Navalny is trying to change the system and is being punished for it."