Russian investigators detained a lawyer who has worked for jailed Russian opposition leader Alexei Navalny and searched the homes of two others, allies of Navalny said on Friday.

They said the three lawyers were being investigated on suspicion of belonging to an extremist group, and accused authorities of opening the case against them in order to further isolate the imprisoned Navalny.

“This morning, police raids are taking place at the homes of three of Navalny’s lawyers. One of them is detained, and we cannot get hold of the other two,” Navalny aide Maria Pevchikh posted on social media platform X.

“Navalny is now left without any legal defence and representation.”

With the help of his lawyers, Navalny, 47, has maintained an active presence on social media and lodged frequent complaints against his treatment in the penal colony in the Vladimir region, east of Moscow, where he is being held.

He is due to be moved soon to a different, “special regime” colony after being convicted in August of a range of new charges relating to “extremist” activity and sentenced to an additional 19 years, on top of 11-1/2 years he was already serving.

Navalny rejects all accusations against him as politically motivated and designed to silence his criticism of President Vladimir Putin.

Navalny’s supporters said one of his lawyers, Igor Sergunin, was detained, and two others, Vadim Kobzev and Alexei Liptser, had their homes searched.

No one was picking up the phone at the office of Sergunin’s law firm in Moscow. There was no word on the cases from Russia’s Investigative Committee.

Navalny aide Leonid Volkov posted on X that the three lawyers faced up to six years in prison if found guilty of belonging to an extremist group, “just for being Navalny’s lawyers”.

“This is an act of intimidation with a clear intention to strengthen Navalny’s isolation from the outer world,” Volkov said.

He said it would mean that after Navalny’s expected transfer to the new penal colony, “his lawyers will not be able to visit him there or even to find out his whereabouts if they’re locked up themselves”, a prospect that Volkov described as “terrifying”.

Navalny has been in prison for the past 998 days since being arrested in 2021 on his return from Germany, where he had been treated after being poisoned with a nerve agent in Siberia.

The Kremlin denied trying to kill him, and refuses to comment on his case or his treatment by prison authorities.