MOSCOW (Reuters) - Russian authorities on Thursday froze a slew of bank accounts linked to jailed opposition politician Alexei Navalny as part of a money laundering investigation that his allies say is a trumped-up attempt to cripple his political movement.

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The move comes ahead of a series of planned nationwide demonstrations on Saturday being organized by Navalny’s allies to protest against the exclusion of opposition candidates from a Moscow election next month.

Similar protests in the Russian capital in recent weeks have led to mass arrests and prompted a wider crackdown on anti-Kremlin activists who have had their homes searched and been handed short jail terms or listed as suspects in a more serious investigation into what the authorities call mass unrest.

Russian investigators said in a statement on Thursday that they had frozen the bank accounts of Navalny’s anti-corruption foundation, those of another organization, and those of more than 100 linked individuals and legal entities.

Kira Yarmysh, Navalny’s spokeswoman, said on Twitter that investigators had also frozen the bank accounts of Navalny’s campaign headquarters across the country.

Masked police officers searched the Moscow offices of Navalny’s anti-corruption foundation as well as the homes of several activists on Thursday taking away computers and documents.

Investigators said they had also summoned some of the foundation’s employees for questioning.

The crackdown came after investigators opened a criminal investigation on Saturday into the alleged laundering of 1 billion rubles ($15.31 million) by Navalny’s foundation.

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

Navalny is currently in jail for violating Russia’s tough protest laws after calling for people to demonstrate in central Moscow over the exclusion of opposition candidates from a local election next month.