MOSCOW — Lyubov Sobol, a lawyer for Aleksei Navalny’s Anti-Corruption Foundation (FBK), has been detained by police for unknown reasons just hours ahead of planned nationwide protests to demand the immediate release of the jailed opposition politician.

“The police carried out an ‘interception’ plan, pulling Lyubov Sobol out of a taxi near the Avtozavodskaya metro station. According to her, many officers in uniforms were involved in her detainment. It is not clear where they are taking her,” Sobol’s lawyer, Vladimir Voronin, tweeted on April 21.

Last week, Sobol was handed a one-year suspended sentence of correctional labor for illegally forcing her way into the apartment of Federal Security Service (FSB) officer Konstantin Kudryavtsev in December, hours after Navalny had published a recording of what he said was a phone conversation with Kudryavtsev.

During the 49-minute phone call, in which Navalny posed as an FSB official conducting an internal review, Kudryavtsev described details of an operation to poison the Kremlin critic in August.

Sobol, who went to Kudryatsev’s apartment building to question him, rejected the charge, saying the case was filed to silence her.

Navalny was arrested on January 17 upon his return to Russia from Germany, where he received life-saving treatment for a poisoning attack in Siberia in August.

He has insisted that his poisoning with a Soviet-style chemical nerve agent was ordered directly by Russian President Vladimir Putin. The FSB and the Kremlin have denied any role in the poisoning, despite Kudryavtsev’s comments.

In February, a Moscow court ruled that, while in Germany, Navalny had violated the terms of parole from an old embezzlement case that is widely considered as being politically motivated. Navalny’s 3 1/2-year suspended sentence from the case was converted to a jail term, though the court said he will serve 2 1/2 years in prison given time already served in detention.

The United States and the European Union have imposed sanctions on Russia over the Navalny affair and its crackdown on protesters.

Last month, Sobol said she plans to run for parliament’s lower chamber, the State Duma, in September elections.

Sobol is currently under house arrest in another case. She and several other associates and supporters of Navalny were charged with violating sanitary regulations during unsanctioned rallies in January to protest Navalny’s incarceration.