(Adds new searches, quotes, Pavlov's release)
MOSCOW, April 30 (Reuters) - Russia has opened a criminal investigation against a lawyer who is defending jailed Kremlin critic Alexei Navalny's Anti-Corruption Foundation (FBK) in an extremism case, and security forces searched and briefly detained him on Friday.
The investigation into lawyer Ivan Pavlov follows mounting pressure by the Russian authorities on the FBK and Navalny's network of political campaign offices across Russia.
In another setback for Navalny's team, Russia's financial monitoring agency said it had added his network of campaign offices to a list of organisations involved in "terrorism and extremism".
"I was interrogated as a suspect," Pavlov told reporters outside a hotel in Moscow. He walked out unguarded and headed to another interrogation with Russia's Investigative Committee.
Pavlov said he had been accused of disclosing classified information relating to an ongoing investigation against one of his clients, former journalist Ivan Safronov.
The Investigative Committee declined 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.
Pavlov's specialist legal areas include treason and espionage. The offence he 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."
Russian security forces also raided Pavlov's wife home and the office of his legal team in St Petersburg, his colleagues said on social media. (Reporting by Maria Tsvetkova, additional reporting by Dmitry Antonov; Editing by Tom Balmforth, John Stonestreet and Timothy Heritage)
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