Russia’s leading opposition leader was detained for the third time this year as he launched his campaign to replace President Putin in the Kremlin.
MOSCOW — The Russian opposition politician Aleksei A. Navalny was convicted and sentenced to 20 days in jail by a Russian court on Monday for repeated violation of rules governing public demonstrations — a term long enough for him to miss a major rally he and supporters had scheduled for Saturday.
Over the past two weeks, Mr. Navalny held several well-attended public events in major Russian cities in what he and his staff are calling a presidential campaign. Russia’s Central Election Commission has said, however, that he cannot legally run for president because of a prior criminal conviction for embezzlement in the theft of timber from a state company, Kirovles.
Over the past year, Mr. Navalny turned into the pre-eminent critic of Russia’s president, Vladimir V. Putin, exposing endemic corruption among top-level government officials in a series of popular videos.
Mr. Putin has not yet officially announced that he will run for another term, but he is widely expected to do so.
Mr. Navalny was detained by police officers on Friday as he left his Moscow apartment to attend a rally in Nizhny Novgorod, a city 260 miles east of Moscow, the capital. He was in custody until the scheduled end of the rally, then was released after he pledged to appear in court on Monday.
Khyzyr Mussakaev, a judge in the Simonovsky district court in Moscow, found him guilty of violating the law on public demonstrations and ordered him held for the third time this year.
“Mr. Putin is so scared of our meetings in the regions that he decided to make himself happy with a small gift for his jubilee,” Mr. Navalny said in a tweet posted to his Twitter account.
In a video message to his supporters he called the sentence “completely unlawful.”
Leonid M. Volkov, his campaign chief, was given a similar punishment and announced on Twitter that he would begin a hunger strike.
Despite the court’s decision, Mr. Navalny’s supporters said they would continue a series of campaign events across Russia and that the next rally, scheduled for Saturday in St. Petersburg, Russia’s second-largest city, would go on as planned. They encouraged Russians nationwide to apply for permits to hold similar demonstrations that day in their own towns and cities.
