MOSCOW -- Police on Friday arrested a top ally and two employees of Alexei Navalny, the Russian opposition leader who over the summer narrowly survived a nerve-agent poisoning.
The arrests highlighted the extraordinary legal pressure that members of his opposition group face in Russia, which has persisted for years, and the heightened sensitivity of authorities toward any activism related to the poisoning.
Earlier this month, Navalny, a leading critic of Russian President Vladimir Putin, and Bellingcat, an open-source investigative outlet, released a report and videos identifying members of what they said was a Russian intelligence agency squad sent to trail and then assassinate Navalny during a trip to Siberia.
But the operation was bungled badly and its secrecy blown by information the team members left in telephone records and databases of airplane passengers, according to Bellingcat.
The accusations of a potentially lethal, almost cartoonish, plot to poison the Kremlin critic by placing nerve agent on his underpants have punctured the aura of invincibility and professionalism of one of Russia's premier intelligence agencies, the Federal Security Service. The Kremlin has conceded that agents trailed Navalny during the trip to Siberia, but it has denied they played any role in the poisoning.
Navalny, who is now recovering in Germany, has taken an active role in investigating the assassination attempt. At least four activists who drew attention to the operation have been arrested.
On Monday, Navalny published online a recording of a phone call in which he said he tricked a chemical weapons expert with the security service, Konstantin Kudryavtsev, into a confession by pretending to be a superior officer.
There was no independent confirmation that Navalny had indeed spoken to Kudryavtsev or that a man by that name had served on a death squad. The Federal Security Service, a main successor to the KGB, took the unusual step Monday of issuing a statement asserting that Navalny's call was a forgery.
In Moscow on Monday, Navalny's top ally, Lyubov Sobol, tried to confront Kudryavtsev at his apartment. The police arrested Sobol but then released her after fining her 1,000 rubles, or about $13, for disobeying a police officer.
Before dawn Friday, police raided Sobol's home and took her into custody again. Ivan Zhdanov, director of Navalny's Anti-Corruption Foundation, wrote on Twitter that she is now under investigation for a more serious offense of breaking and entering, which could lead to a two-year prison sentence.
Also Friday, authorities detained for questioning Akim Kerimov and Olga Klyuchnikova, two employees of Navalny's YouTube channel, Navalny Live, according to a report by the channel.
This month, Clarissa Ward, the chief international correspondent for CNN, visited the apartment of another man Bellingcat had identified as an assassin. The man declined to be interviewed. Ward was not arrested.
The Kremlin has not confirmed that the men whom Ward and Sobol tried to approach are security agents.
This week, in another crackdown on activism related to the poisoning, police briefly detained filmmaker Vitaly Mansky for protesting in front of the security service headquarters in Moscow while holding a pair of checkered blue underpants, symbolically implicating the spy agency in the poisoning.