"I was very concerned to see reports of police harassment and arrests of politicians and peaceful demonstrators in Russia," commission president Jose Manuel Barroso said through a spokesman in a video statement on the body's web site.
"The right to peaceful free speech and assembly are basic, fundamental human rights, and I very much regret that the authorities found it necessary to take such heavy-handed action," the statement said.
Baton-wielding riot police detained dozens of activists rallying against President Vladimir Putin in Moscow on Saturday and St. Petersburg on Sunday. Many of those detained had been protesting peacefully before police carried them off to vans.
City Hall had given permission for a rally in Moscow, but not for a march.
French Foreign Minister Bernard Kouchner told RTL radio that Russia should provide an "explanation."
"I am surprised by this violence. To my knowledge, the world chess champion was not a threat to Russia's security," Kouchner said. "Russia wants to take its place, a large place, in contemporary history, and for that it has to evolve and not seem menacing."
The British Foreign Ministry issued a somewhat softer statement, reminding Moscow that "the right to peaceful protest and adherence to the rule of law are two vitally important components of any democratic process."
Washington on Sunday condemned the arrest of opposition leader Garry Kasparov, accusing the Russian government of stifling dissent.
Garry Kasparov, leader of The Other Russia opposition coalition, was detained in Moscow on Saturday and immediately sentenced to five days in prison for resisting arrest. The Meshchansky District Court ruled late Monday that Kasparov's detention was legal and that he should serve out the five-day sentence
Numbers from Moscow City Court indicate that a fair number of people have been detained.
Legal proceedings were initiated against about 50 Other Russia activists suspected of disturbing the peace during Saturday's rally, said Anna Usachyova, a court spokeswoman.
In St. Petersburg on Sunday, police detained "several dozen" activists, a city police spokesman said.
Other Russia spokeswoman Lyudmila Manina said, however, that 200 to 300 people were detained there. Regarding the discrepancy, police spokesman Vyacheslav Stepchenko said The Other Russia was trying to "sensationalize" the news.
Among those detained were Boris Nemtsov and Nikita Belykh, leaders of the Union of Right Forces party, who are both running on the party's list for the Duma elections. They were later released.
None of four Moscow Times reporters witnessed any police beatings in Moscow on Saturday. Physical contact between police and activists seemed to be limited to pulling suspects away and pushing them into vans.
Kasparov, who has been denied access to visitors, according to his spokeswoman, Marina Litvinovich, is due to be released from city police headquarters on Petrovka Ulitsa on Thursday evening.
Vladimir Ryzhkov, an independent State Duma deputy and a participant in Saturday's march, tried on Sunday night and Monday morning to visit Kasparov. Although his job allows him to do so, police refused access, a spokeswoman for Ryzhkov said, adding that Ryzhkov was suing Moscow police chief Vladimir Pronin.
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