Russian investigators said on Thursday they had opened a criminal case into Leonid Volkov, a close ally of jailed Kremlin critic Alexei Navalny, hours before a court was due to hear an appeal against Navalny’s own jailing.

The case against Volkov, currently outside Russia, is part of a police crackdown targeting Navalny’s allies after tens of thousands of people took to the streets on Saturday to demand the Kremlin release Navalny from jail.

A court at 1100 GMT later on Thursday is due to hear an appeal into the jailing of Navalny, who is serving a 30-day stint for alleged parole violations which he denies.

The Investigative Committee, which probes serious crimes, accused Volkov in a statement of urging teenagers to take part in what it said were illegal protests on Saturday.

A protest monitor has said that police detained close to 4,000 people at the demonstrations in Moscow and dozens of other cities after saying they were unauthorised.

The Interfax news agency cited a source on Thursday as saying that police had detained a fugitive 20-year-old Chechen man who was shown brawling violently with riot police in footage of Saturday’s protests.

Navalny’s supporters plan to hold new rallies this Sunday which the authorities have also declared illegal.

Late on Wednesday, police carried out mass searches at the homes of Navalny’s supporters and other properties linked to him, detaining several people, including his brother Oleg for allegedly breaching COVID-19 safety restrictions.