MOSCOW — The police in Moscow arrested more than 400 people who had gathered outside City Hall on Saturday to protest what they call unfair elections and demand that opposition candidates be allowed to run for city government.
In anticipation of the unauthorized demonstration, the authorities on Wednesday arrested Aleksei A. Navalny, a foe of President Vladimir V. Putin and a major opposition leader, and sentenced him to 30 days in jail.
Other prominent opposition politicians — including Ilya Yashin, Dmitry G. Gudkov and Ivan Zhdanov — have also been detained. A post on the Facebook page of Mr. Yashin, a street activist, said 10 masked police officers had removed him from his apartment in Moscow overnight before the Saturday demonstration.
The Moscow City Council has 45 seats and is responsible for a very large municipal budget. It is controlled by the pro-Kremlin United Russia party. All of its seats, which have a five-year-term, are up for election on Sept. 8.
To compete in the elections, candidates not endorsed by a political party must collect about 5,000 signatures, depending on the size of their district. Election officials have so far registered nearly 200 candidates, all of whom are largely supportive of Mr. Putin.
But Moscow’s electoral commission has refused to register several prominent opposition candidates, saying that they had failed to collect enough valid signatures to place them on the September ballot. The candidates, including allies of Mr. Navalny, said the signatures were genuine.
The decision by the electoral authorities to bar some opposition candidates has already sparked days of demonstrations this month. The election dispute comes as the Kremlin is struggling with how to deal with rising opposition in the capital of 12.6 million people.
The protest, which was called by Mr. Navalny, appeared intended also to raise the pressure on Russia’s tightly-controlled political system at a time when Mr. Putin’s rating has dropped because of discontent over years of falling real incomes.
The number of arrests, 435 by Saturday afternoon, was reported by OVD-Info, an independent monitor that tracks data from police precincts. The police could be seen using pepper spray on some crowds.
One of those detained, Alexander Latyshev, 45, told Reuters that he had come to Moscow from the nearby Vladimir region to discuss business with an associate and been randomly arrested by the police.
“I was just sitting on a bench” when they took him, he said from inside a police bus.
There was a heavy police presence at the Moscow mayor’s office on Tverskaya Street, one of Moscow’s main thoroughfares, with police trucks and buses parked in the building’s courtyard and other buses positioned nearby to take detainees away, according to The Associated Press.