Russian opposition leader Alexei Navalny said that at least 200 raids were carried out against his supporters in 43 cities.
"Raids are underway in 43 cities in more than 200 places because they (the investigators) have come to the headquarters coordinators, their relatives, employees, and former employees," Navalny's spokesperson, Kira Yarmysh, told Euronews.
She said the raids took place around the same time so that activists did not have time to warn each other.
The searches were carried out just days after Russia's ruling party lost a third of its seats in Moscow's city legislature.
Navalny had been jailed for 30 days after calling for protests in support of free elections after opposition candidates were prevented from running for the Moscow legislature.
The searches are related to a money-laundering investigation against the Navalny's Anti-Corruption Foundation (FBK), but the opposition activists deny that their guilt. They've called the raids "political persecution" associated with the recent election results.
"The Kremlin is afraid of any consolidated action. Over the past weekend, there were elections throughout the country that ended, without a doubt, with a 'smart vote' victory not only in Moscow but also in the regions. This frightened Vladimir Putin personally, the presidential administration, and that’s why they gave the order to go to all our headquarters," said Yarmysh, referring to activist calls to vote against the ruling party.
On August 9, investigators blocked money from the accounts of the organisation and regional headquarters of Navalny.
"Of course, this will hit us very hard. This is by far the biggest blow to FBK and to the network of regional headquarters that has ever been in our entire existence. But it is obvious that the greater the strength of our action, the greater the strength of the reaction," Yarmysh explained of the raids.
Video posted to social media and CCTV footage showed masked men raiding the offices.
Golos, a Russian non-profit organisation that monitors elections, reported that the coordinator of their Saratov branch, Alexander Nikishin, had his apartment raided.
Yelena Ivanova, who is editor in chief of Svobodnye Novosti news agency where Nikishin also works, told Euronews that she thought it was related to the elections that took place on Sunday.