Russian authorities on Thursday froze a slew of bank accounts linked to jailed opposition politician Alexei Navalny as part of a money laundering investigation, Kira Yarmysh, his spokeswoman, and Russian investigators said.

Russia’s Investigative Committee announced during protests in Moscow last weekend that it had opened a criminal case into the laundering of 1 billion rubles ($15.3 million) by Navalny’s Anti-Corruption Foundation (FBK). Authorities raided the FBK’s office in Moscow as part of the investigation, the committee said Thursday.

More than 100 private and legal accounts have been frozen, investigators said after Yarmysh said that his foundation’s and regional offices’ accounts were blocked. Accounts frozen included those associated with the FBK, some personal accounts of allies and accounts belonging to Navalny’s headquarters.

“Searches are being carried out at a number of FBK employees’ residences, the organization’s office and other locations as part of the criminal case today,” the committee said in a statement.

An unspecified number of staffers have been summoned for questioning, the committee said hours after early-morning reports that authorities raided the homes of three FBK lawyers.

Navalny and his allies say the foundation, which has published a slew of embarrassing investigations into government officials, is transparently financed from public donations.

He is serving a 30-day jail sentence as his allies stage protests every weekend against authorities’ decision to bar opposition candidates from a Moscow vote next month.

Reuters contributed reporting to this article.