Russian police raided the Moscow offices of jailed Kremlin critic Alexei Navalny’s group on Wednesday and came to search several other properties, including a flat where his wife was, one of his allies said.

The searches come after tens of thousands of Navalny’s supporters took to the streets on Saturday to call on the Kremlin to release him from jail where he is serving a 30-day stint for alleged parole violations that he denies.

Police had said the protests were illegal and detained close to 4,000 people. More than a dozen criminal cases have been opened. Navalny’s allies plan to hold another rally this Sunday.

Ivan Zhdanov, director of Navalny’s Anti-Corruption Foundation, said police appeared to be conducting the searches as part of an investigation into calls made to hold a protest that flouted restrictions imposed over the COVID-19 pandemic.

Zhdanov wrote on Twitter that Navalny’s apartment in northern Moscow was being searched.

“A lot of ‘heavies’ in masks. They started breaking down the door,” Zhdanov said, adding that Navalny’s brother, Oleg, was inside the property.

At another location, Zhdanov posted video showing Yulia Navalnaya, the Kremlin critic’s wife, telling police to wait for her lawyer to arrive as they banged loudly at the door.

Police also searched the offices of Navalny’s Anti-Corruption Foundation, he said. Photos on social media showed around 20 masked men waiting to gain entry.

Navalny has not yet returned home since being poisoned last summer, as he was arrested immediately on his return to Russia from Germany, where he had been recovering.