Russian opposition leader Alexei Navalny was jailed for 30 days on Wednesday for calling an unauthorised protest.
Mr Navalny, an open critic of the Kremlin, planned to lead a march in Moscow this weekend to protest against the exclusion of several candidates in a local election in September.
His spokeswoman, Kira Yarmysh, announced the sentence on Twitter. It is the maximum sentence for the charge.
Mr Navalny was detained by riot police as he left for a morning jog.
“I left for a run and to buy my wife flowers," he tweeted. "It’s her birthday today, so happy birthday, Yulia.”
The State Investigative Committee later announced it was opening a criminal investigation over possible interference in the work of election committees.
Local election officials decided to exclude almost all critical voices from September’s city elections.
They claim the candidates had not collected enough genuine signatures to run.
This month several of the excluded candidates held a protest. Last week a second protest was attended by more than 200,000 people, making it the largest opposition rally for years.
Last year, Mr Navalny was jailed for three weeks for organising anti-Kremlin protests.
