Police in Moscow have detained more than 300 people at a Muslim prayer room in the Russian capital, including 170 foreigners.
Police did not say why the people had been detained during the police action on June 7.
Police said Islamist literature had been confiscated to check for extremist content.
Reuters said it is the third such raid targeting Muslim places of worship in Moscow or St. Petersburg this year.
It comes after President Vladimir Putin ordered a crackdown on radical Islamists ahead of next year's Winter Olympics in Sochi.
Putin told a meeting of security force officers earlier on June 7 that the "fight against corruption, crime and the insurgency has to be carried out harshly and consistently."
He said "the situation in the North Caucasus should be kept under particular control."
Based on Reuters and Itar-tass reporting