Russian opposition leader Alexei Navalny and his supporters said that police raided the apartment of an associate Friday morning and detained her for questioning.
"Today, police came to Lyubov Sobol's apartment at 7 am," Navalny's Anti-Corruption Fund chairman Ivan Zhdanov said in a tweet.
Zhdanov and Navalny’s spokesperson, Kira Yarmyash, said that the phone of Sobol was turned off and they did not know anything of her whereabouts.
Sobol has announced her plans to run in parliamentary elections next year.
Navalny said on Twitter that the police raid was a response to a telephone call he made Monday to a poisoning expert with the FSB. On the call he said he impersonated an official with the Kremlin's Security Council and got the expert to admit that Navalny was poisoned back in August.
According to Navalny, Sobol, a lawyer by training, attempted to speak to the FSB agent, who he named as Konstantin Kudryavtsev.
The FSB has denied Navalny's allegations of poisoning.
However, Western governments have said Navalny was poisoned with Novichok, a Soviet-designed nerve agent.