Russia opened a criminal case on Friday against Lyubov Sobol, an ally of Kremlin critic Alexey Navalny, over accusations she had violently entered a flat that her supporters said was linked to a secret agent involved in a plot to kill Mr. Navalny.
The move against Ms. Sobol is the latest in a clampdown on the Kremlin’s opponents before next year’s parliamentary election. Ms. Sobol aims to run for office, although outspoken critics of the Kremlin are often prevented from standing.
Ms. Sobol was detained for 48 hours after questioning, Mr. Navalny, one of the Kremlin’s fiercest opponents, wrote on Twitter.
Russia’s Investigative Committee, which handles serious crimes, said on its website on Friday it had launched a criminal case against Ms. Sobol. It did not mention any detention.
Ms. Sobol’s supporters and the authorities gave different accounts of events leading up to Friday’s actions.
Her supporters said she rang the doorbell on Monday of an apartment owned by the family of a man who Mr. Navalny has said was an FSB security service officer involved in a bungled attempt to poison him using a nerve agent.
The FSB has dismissed Mr. Navalny’s account of the poisoning.
In its account, the Investigative Committee said Ms. Sobol and several others tried to gain entry to an old woman’s flat in Moscow, wearing uniforms used by the state consumer health watchdog.
It accused her of tricking a delivery courier to enter the apartment block before barging into the woman’s flat when she opened the door. It said Ms. Sobol was suspected of using violence to enter illegally, an offence that can carry a jail term of up to two years.
Mr. Navalny wrote on Twitter: “They are locking up the mother of a small child for two days to tell everybody: don’t dig into this case. Don’t dare to mess with our killers and poisoners and knock on their doors. These killers are untouchable.”
Germany and other Western countries say Mr. Navalny was poisoned with a Soviet-style Novichok nerve agent in a murder attempt. The Kremlin has repeatedly denied the accusations.
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