MOSCOW — Several thousand people protested Monday night against Prime Minister Vladimir Putin and his party, which won the largest share of a parliamentary election that observers said was rigged.
It was perhaps the largest opposition rally in years and ended with police detaining some of the activists.
A group of several hundred marched toward the Central Elections Commission near the Kremlin, but were stopped by riot police and taken away in buses. The total number of those detained was not immediately available.
Estimates of the number of protesters at the rally ranged from 5,000 to 10,000. They chanted "Russia without Putin" and accused his United Russia party of stealing votes.
United Russia took about 50 percent of Sunday's vote, a result that opposition politicians and election monitors said was inflated because of ballot stuffing and other vote fraud. It was a significant drop from the last election, when the party took 64 percent.
Pragmatically, the loss of seats in parliament appears to mean little. Two of the three other parties winning seats have been reliable supporters of government legislation.
But it is a substantial symbolic blow to a party that had become virtually indistinguishable from the state itself.
It also has energized the opposition and poses a humbling challenge to the country's dominant figure in his drive to return to the presidency.
Mr. Putin, who became prime minister in 2008 because of presidential term limits, will run for a third term in March, and some opposition leaders saw the parliamentary election as a game-changer for what had been presumed to be his easy stroll back to the Kremlin.
Also Monday, more than 400 Communist supporters gathered to express their indignation over the election, which some called the dirtiest in modern Russian history. The Communist Party finished second, with about 20 percent of the vote.
"Even compared to the 2007 elections, violations by the authorities and the government bodies that actually control the work of all election organizations at all levels, from local to central, were so obvious and so brazen," said Yevgeny Dorovin, a member of the party's central committee.
Mr. Putin appeared subdued and glum even as he insisted at a Cabinet meeting Monday that the result "gives United Russia the possibility to work calmly and smoothly."
Although the sharp decline for United Russia could lead Mr. Putin and the party to portray the election as genuinely democratic, the wide reports of violations have undermined that attempt at spin.
Many Russians came to despise United Russia, seeing it as the engine of endemic corruption. The election showed voters that they have power despite what election monitors called a dishonest count.
Analysts suggested the vote was a wake-up call to Mr. Putin that he had lost touch with the country. In the early period of his presidency, Mr. Putin's appeal came largely from his man-of-the-people image: candid, decisive and without ostentatious tastes.
But he seemed to lose some of the common touch, appearing in well-staged but increasingly preposterous heroic photo opportunities - hunting a whale with a crossbow, fishing while bare-chested, and purportedly discovering ancient Greek artifacts while scuba diving.
And Russians grew angry at his apparent disregard of the country's corruption and massive income gap.