The chief of Russian opposition leader Aleksei Navalny's campaign office in the Far Eastern city of Khabarovsk has been detained.
Aleksei Vorsin wrote on Facebook that officers of the regional police Center for Measures against Extremism brought him to a police station on June 7.
There, he was told that his detainment was linked to his public calls to Russians to take part in anticorruption demonstrations that Navalny and his backers are planning to hold nationwide on June 12.
Vorsin said that police had visited him on June 6 and asked him to go with them to a police station, but that he refused because they had no warrant or written subpoena.
If a court rules that Vorsin made public calls for an unsanctioned protest, he could be jailed for up to 30 days.
Kremlin foe and anticorruption crusader Navalny is trying to build momentum after organizing protests that drew large crowds on March 26.
He is seeking to run in a March 2018 election in which President Vladimir Putin is widely expected to seek and secure a new six-year term.