Russian police raided the home of opposition activist Lyubov Sobol early on Friday morning before detaining her for further questioning, Kremlin critic and close ally Alexei Navalny has said.

The dissident lawyer posted a video on Twitter of police banging at Sobol's door, followed by footage of the officers loitering outside the Moscow apartment and then covering the security camera with duct tape.

Ivan Zhdanov, head of Navalny's Anti-Corruption Fund, later wrote on Twitter that investigators launched a probe into trespassing "with the use of violence or a threat to use it" after Sobol rang the doorbell of an alleged Federal Security Service (FSB) agent in Moscow this week.

Navalny says the agent took part in a botched plot to poison him in August.

FSB suspicions

Navalny said he had tricked the agent, an alleged chemical weapons expert named Konstantin Kudryavtsev, into admitting that the domestic intelligence agency had sought to kill him this summer by placing poison in his underwear.

The FSB has dismissed Navalny's allegations as a provocation and Russian President Vladimir Putin has suggested if the Kremlin had poisoned the fierce critic, he would be dead by now.

Sobol's phone has been turned off since her arrest and both Navalny's spokeswoman, Kira Yarmyash, and the head of Navalny's foundation, Ivan Zhdanov, said they did not know where she was.

Sobol's husband and daughter, who can be heard crying in the video, have been allowed to leave the flat.

Tit-for-tat sanctions

The European Union issued sanctions against six Russian officials in October, including the head of the FSB internal security agency, arguing that the Kremlin's security services must have been complicit in poisoning Navalny two months before.

Navalny fell ill during a flight from Siberia to Moscow in August and was hospitalized in the city of Omsk before being transported to a Berlin hospital. The anti-corruption campaigner has been receiving treatment in Germany since then.

Russia has since responded to the sanctions by imposing similar measures on its European counterparts.

Earlier this week, Navalny released a recording in which he claimed to have duped a Russian security agent into revealing details about the attempt on his life.

jsi/mm (AFP, Reuters)