Russian authorities have filed criminal charges against one of the country's top human rights lawyers who is defending jailed Kremlin critic Alexei Navalny's Anti-Corruption Foundation (FBK) in an extremism case.
Security forces searched and briefly detained Ivan Pavlov on Friday morning.
He was later charged with disclosing classified information on an investigation and summoned to appear in a Moscow court, his legal team said.
Pavlov, 50, is well known inside Russia for taking on high profile and often politically sensitive cases in which he finds himself representing people accused by the Russian state of everything from treason to espionage.
The investigation into him follows mounting official pressure on the FBK, a Navalny-linked organisation that has produced a slew of high profile and sometimes embarrassing investigations into official corruption.
Some of the targets of its exposes have sued it and disputed its findings.
It comes at a time when Navalny's movement and network of political campaign offices across Russia is under unprecedented pressure designed to end its activities.
Navalny, President Vladimir Putin's fiercest political rival, is serving a two and a half year jail sentence for parole violations on an earlier embezzlement conviction that he says was politically motivated.
In another setback for Navalny's team, Russia's financial monitoring agency said on Friday it had added his network of campaign offices to a list of organisations involved in "terrorism and extremism".
"A search was carried out now and my lawyer documents were illegally seized," Pavlov told reporters outside a Moscow hotel.
He said he was being investigated over an ongoing case against one of his clients, former journalist Ivan Safronov.
Russia's Investigative Committee declined to comment.
Pavlov was due to lead a legal team representing the FBK in a court hearing considering a request from the Moscow prosecutor to declare the group an extremist organisation.
The main hearing is scheduled for May 17.
The offence Pavlov is accused of is punishable by up to three months in jail, Pavlov's legal team said.
"Of course, this is an element of pressure because if he's found guilty of committing a deliberate crime he would be deprived of his lawyer status and therefore would not be able to continue his professional activity," said Dmitry Katchev, one of Safronov's lawyers.
Kremlin spokesman Dmitry Peskov said: "We don't have any information, we don't know the reason for the arrest and how it happened, what this lawyer is accused of."
Australian Associated Press