Kremlin critic Alexei Navalny was jailed for 30 days on Wednesday, his spokeswoman said, ahead of a march he planned to lead in Moscow in protest at the exclusion of several opposition-minded candidates from a local election in September.
Police detained Navalny as he left his home earlier on Wednesday, accusing him of calling for an unauthorized rally, his spokeswoman Kira Yarmysh said.
Navalny's sentence follows a similar protest last weekend ahead of the election for the Russian capital's legislature. A monitor said more than 20,000 people had attended that protest.
Election officials barred the candidates for what they said was their failure to garner enough genuine signatures from voters to qualify to run, an allegation they rejected as false.
The candidates say the real reason they were excluded was because they were trying to challenge control over the legislature exercised by allies of President Vladimir Putin.
Navalny's supporters are among those barred from running in the election.
Speaking at Saturday's protest, Navalny gave election officials a week to register the excluded candidates and urged protesters to hold an unauthorized protest outside Moscow city hall this Saturday if they failed to do so.
"I left home for a jog and to buy my wife flowers for her birthday... There was a small bus of riot police near my stairwell and I was detained," Navalny said in a video message on Instagram after his arrest.