MOSCOW - President Vladimir V. Putin's chief political foe was convicted along with his brother Tuesday in a fraud case widely seen as a Kremlin vendetta, triggering one of Russia's boldest antigovernment demonstrations in years.

Police let a few thousand protesters gather outside Red Square for about two hours - a show of relative restraint for authorities, who have little tolerance for dissent - before moving in to break up the unsanctioned rally by pushing protesters toward subway entrances.

The rally came hours after anticorruption campaigner Alexei Navalny was found guilty of what activists said were trumped-up charges and given a suspended sentence of 31/2 years. His younger brother was sent to prison, a move that drew comparisons to the Stalin-era practice of punishing family members of enemies of the state.

The elder Navalny, 38, a lawyer and popular blogger, rose to prominence with his investigations of official corruption and played a leading role in organizing anti-Putin demonstrations in Moscow in 2011 and 2012.

Navalny, who has been under house arrest since February, violated its terms to attend the rally and was rounded up by police as he approached the site. He later tweeted that police drove him home and blocked him from leaving his apartment.

The protesters, who gathered on the Manezh Square outside the Kremlin, chanted: "Russia without Putin!" Some shouted slogans of support for Ukraine.

Scuffles erupted between protesters and pro-Putin activists shouting, "Those who don't like Russia should go to the United States!" - the chants reflecting the Kremlin's depiction of opposition supporters as Western stooges.

Russian authorities usually move quickly to break up opposition protests, and the unusual delay this time may reflect Kremlin concerns about fueling public anger amid the country's economic woes. The ruble has lost about half its value this year, and the economy is heading into recession under the weight of Western sanctions and slumping oil prices.

Police said they detained about 100 protesters; activists said up to 250 were rounded up. Russian law requires demonstrators to get official clearance for rallies. Violators can face prison sentences and heavy fines.

Oleg Navalny, a former executive of the state-owned postal service, has never played a role in the opposition movement. Alexei Navalny and his supporters portrayed the brother's prison sentence as a means of punishing Alexei.

"The government isn't just trying to jail its political opponents - we're used to it," Alexei Navalny said outside court. "We're aware that they're doing it - but this time they're destroying and torturing the families of the people who oppose them."

Political analyst Masha Lipman said it was clear the Kremlin had decided not to make a martyr out of Alexei Navalny.

The Navalnys were convicted of cheating a French cosmetics company and given the same 31/2-year sentence, but only Alexei's was suspended.