Russian authorities have detained three lawyers representing imprisoned opposition leader Alexei Navalny, his aides said on Friday.

Authorities searched the homes of Vadim Kobzev, Igor Sergunin, and Alexei Liptser — all of whom have defended Navalny in the past — as part of a criminal case on charges of participating in an extremist organization.

Ivan Zhdanov, the director of the Anti-Corruption Foundation (FBK) set up by Navalny, said the charges were intended to isolate Navalny completely. 

"That's what all this is being done for: to leave Alexei without legal protection," his spokeswoman Kira Yarmysh added.

"And to send a signal to other lawyers: it is dangerous to defend him and other political prisoners." 

All three lawyers were ordered to be held in pretrial detention until at least December 13, according to reports. 

Navalny says it is a reminder of Soviet times

Kobzev was due in court on Friday to represent Navalny in a lawsuit he has filed against his prison sentence. 

"Information has just arrived that, of course, perfectly characterizes not only my proceedings but also the state of the rule of law in Russia," Navalny told the judge on learning of the probe against his lawyers.

"As in Soviet times, not only political activists and political prisoners but also their lawyers are being persecuted," he added.

All three lawyers were ordered to be held in pretrial detention until at least December 13, reports said.

Russia's most prominent domestic critic of President Vladimir Putin — is serving a 19-year prison sentence and is recognized as a political prisoner by international human rights organizations.

Despite his imprisonment, Navalny has been able to post on social media through his lawyers, who have acted as his conduit to the outside world.

But he is scheduled to be moved to a "special regime" colony — the harshest type of prison reserved for Russia's most dangerous criminals — which will severely restrict his contact with his lawyers and family.

dvv/lo (AP, AFP, dpa, Reuters)