Police arrested more than 2,500 people at dozens of anti-Putin rallies demanding the release of the Russian leader's fiercest critic.
Violent clashes left Alexei Navalny supporters bloodied - drawing condemnation from the UK and other countries - and police were pelted with snowballs during a demonstration in Moscow.
Riot police used force to break up rallies as tens of thousands of protesters defied a ban by authorities and braved bone-numbing temperatures as low as -52C.
Navalny's wife Yulia was among those detained in the capital. She posted an Instagram selfie from the back of a police van, writing: "Sorry for the poor quality.
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