Russia's Federal Security Service, the KGB's main successor, has summoned opposition leader Gary Kasparov for questioning on suspicion of propagating extremism.
Kasparov's aide says investigators want to determine whether the former chess champion, in a radio interview he gave before the recent protests in Moscow and St. Petersburg, made calls for extremist action.
Kasparov received the summons Tuesday as the Kremlin conceded that some police over-reacted when they clubbed unarmed demonstrators and dragged them to waiting police buses.
Kremlin spokesman Dmitri Peskov called the protests marginal, but he also accused foreign media of exaggerating the scale of the demonstrations.
About 2,000 opposition activists participated in each rally, protesting what they contend is President Putin's stranglehold on democracy. Huge numbers of riot police overwhelmed protesters in both cities.
Germany, which holds the rotating European Union presidency, has called the Russian police actions unacceptable, while the United States voiced deep concern over the police response.
Separately, spokesman Peskov sought to dismiss speculation that Mr. Putin will seek an unprecedented third term as president. He said the two-term limit enshrined in Russia's post-Soviet constitution will not be altered.
Some information for this report was provided by AFP, AP and Reuters.