At least 47 people were arrested in Moscow on Friday shortly before the start of an unauthorised demonstration against the policies of Russian Prime Minister Vladimir Putin.
Among the protesters arrested was opposition politician Eduard Limonov, the Interfax news agency reported, citing official sources.
Moscow human rights activist Lev Ponomarev called the actions by the security forces, who were present in great numbers, as "completely disproportionate".
About 200 demonstrators and 50 journalists were to have participated in the protest, according to a police spokesman. Those arrested could face charges for violating laws relating to public assemblies and fines of up to 2,000 rubles ($63).
Protest organisers have accused the police of abusing their power and signalled plans to hold more demonstrations in August.