Moscow police detained dozens of demonstrators late on May 8 -- including opposition Left Front leader Sergei Udaltsov and activist Aleksei Navalny -- as small sporadic protests continued against President Vladimir Putin's rule.
It was the second time Udaltsov and Navalny were detained within a day. Earlier on May 8, they were among dozens of protesters led away by police who broke up a peaceful protest in Moscow.
Udaltsov arrived at the late-night protest in central Moscow after being released earlier in the day and was greeted by dozens of protesters who responded to his arrival by chanting "Russia without Putin," despite the numerous arrests.
Udaltsov stood on a bench and told the gathering: "Moscow is against Putin. Moscow is against crooks and thieves! We will win!"
As he was led away by police, Udaltsov called on demonstrators to "walk further" and to keep their protests going on May 9.
Russian authorities have detained nearly 750 people since May 6 in a crackdown against public dissent as Putin resumed the presidency.
Russia's lower house of parliament confirmed former President Dmitry Medvedev as prime minister on May 8, completing a job swap with Putin that has sparked protests against the two leaders' grip on power.
Activist Aleksei Navalny was among those detained by Moscow police on May 8.
Lawmakers in the Duma, where the Kremlin-allied United Russia party holds a majority, approved Medvedev by a vote of 299-144.
Putin, who had nominated Medvedev immediately after his lavish swearing-in ceremony on May 7, told the Duma after the vote, "I am sure that the new chairman of the government of the Russian Federation will work with all the factions of the State Duma, and the government will listen to everyone."
Putin had served as Medvedev's prime minister after completing between 2000 and 2008 his first two consecutive terms as president allowed by the constitution.
Udaltsov said the protests were proof that pro-democracy forces have not abandoned the struggle. "We have shown that we have not given up and the fight for fair elections and a legitimate government goes on," he said.
"And the harsher the government's reaction toward us, the harsher we will respond, and we will defend ourselves as we have every right to do. If the government is trying to destroy us, we have the right to take a stand, and this will happen sooner or later," he added.
U.S. State Department spokesman Mark Toner said on May 8 that the United States was "disturbed" by the Russian security forces' crackdown on peaceful protesters. He urged the Russian authorities to allow freedom of speech and assembly.
Toner said the State Department was also concerned about reports that some small groups of protesters had attacked Russian law enforcement officials. He called on both sides to refrain from violence.
With reporting by Tom Balmforth in Moscow, and by Reuters, AP, and AFP