MOSCOW — Russia’s most effective anticorruption campaigner and opposition leader was found guilty of embezzlement Thursday and sentenced to five years in prison in a verdict that sent shock waves throughout the country.
The conviction of Alexei Navalny, 37, a leading critic of President Vladimir Putin with a penchant for exposés and cutting jibes, brought sharp criticism from those who believed it to be a politically driven case.
The US ambassador to Russia, Michael McFaul, posted on Twitter: ‘‘We are deeply disappointed in the conviction of Navalny and the apparent political motivations in this trial.’’
A statement by the European Union’s foreign affairs chief, Catherine Ashton, said: ‘‘This outcome, given the procedural shortcomings, raises serious questions as to the state of the rule of law in Russia.’’
Police closed Red Square and blocked off nearby Manezh Square to prevent protesters from gathering in an unsanctioned demonstration against the verdict, but by evening a crowd of several thousand had gathered along the sidewalks of adjoining streets.
The youthful crowd spread out in different directions, making it impossible to gauge its size. In a mood more of disgust than anger, the crowd chanted, ‘‘Navalny!’’ and ‘‘Freedom!’’
The police presence was heavy.
In an unexpected move, prosecutors asked for Navalny to be placed under house arrest until his sentence goes into effect in 10 days, perhaps in an attempt to allow public anger to dissipate. The judge made no public comment on the request, however, and as of Thursday night Navalny remained in jail.
Even before his trial began in April in the city of Kirov, about 550 miles northeast of Moscow, Navalny said that he expected to be convicted of what he and his supporters contended were trumped-up charges. But as he was led into custody, it became clear that those in power in Russia have chosen not to be subtle as they crack down on the opposition.
‘‘This shows to what extent the government is afraid of Alexei Navalny,’’ Yevgenia Albats, chief editor at New Times magazine, said on the Ekho Moskvy radio station. ‘‘I think they did it because it is the main principle of security officers — not to show weakness. If you put the man on his knees, then you must finish him off.’’
Navalny’s case is the most prominent of a series of prosecutions that Russian authorities have launched against their critics since the outbreak of political protest in late 2011, much of it led by Navalny.
Prosecutors asked for a six-year term for Navalny and a lesser term for codefendant Pyotr Ofitserov.
Shortly after noon, Judge Sergei Blinov sentenced Navalny to five years and Ofitserov to four. He ordered both men to immediately be taken into custody. Ofitserov’s wife cried. Navalny looked shaken, but he tweeted to his supporters: ‘‘OK. Don’t get bored here without me. And most important — don’t dawdle.’’
Human rights advocates denounced the sentence. Navalny is a political prisoner, said Alexander Cherkasov, the leader of the Memorial Human Rights Center. Svetlana Gannushkina, the head of the Civil Support Committee, told the Interfax news agency that the sentence will have destructive consequences for the country.
Former Soviet president Mikhail Gorbachev called the prosecution and verdict ‘‘very depressing,’’ in a message on his foundation’s website.
“The case, unfortunately, confirms that we don’t have an independent court system,’’ Gorbachev wrote.
The sentencing hearing Thursday was attended by a pack of supporters and television crews, and it was live-streamed on a website. Navalny, smiling and relaxed and sending out tweets, had left Moscow by overnight train Wednesday. Among those present in the courtroom were his wife, his father, and opposition politician Boris Nemtsov.
After Navalny was led out of the courtroom, his wife, Yulia, addressed supporters and journalists, striking a defiant tone.
‘‘If someone hopes that his investigation will stop, it won’t,’’ she said. ‘‘The anticorruption foundation will continue its work, and we really hope for your support. The main thing we can do now is to work and show our solidarity with Pyotr and Alexei. I do believe everything will be good. We will win. And, please, believe that everything will be great.’’
Navalny was charged with theft from a deal he arranged in 2009, when he was an assistant to the governor in Kirov. He found a middleman to buy timber from a struggling logging company. Because the middleman made a profit on the timber, the prosecution charged that Navalny had effectively deprived the lumber company of nearly $500,000, by getting it to agree to sell below market value.