Russian police arrested dozens of activists, including opposition leader Boris Nemtsov, to stop a new protest alleging that elections were rigged in favour of Vladimir Putin's ruling party.
Helmeted riot police and interior ministry troops deployed in force for the rally in central Moscow which was held after an unusually large thousands-strong protest on Monday startled the authorities.
Opposition supporters shouted "Shame on you fascists!" and "Russia without Putin" in a tense stand-off with members of pro-Kremlin youth who also descended on the site of the protest in central Moscow.
Police roughly hauled dozens of opposition supporters into vans parked near the protest in central Moscow, an AFP correspondent said. A police spokesman told the ITAR-TASS news agency that over 100 people were arrested.
The protests come after Sunday's parliamentary election was won by Putin's United Russia with a sharply reduced majority but which the opposition said was marred by mass violations as the party sought to keep its dominance.
International observers have said there were major violations and that the State Duma polls were slanted in favour of United Russia, comments backed by US Secretary of State Hillary Clinton who said she had serious concerns.
"As we have seen in many places, and most recently in the Duma elections in Russia, elections that are neither free not fair have the same effect," Clinton said in Lithuania.
The Russian foreign ministry described Clinton's comments as "unacceptable" while President Dmitry Medvedev said it was "none of their business" what Russia's political system looked like.
Olga Shorina, spokeswoman for the Solidarnost (Solidarity) opposition movement, told AFP that 10 riot police detained Nemtsov, who is a former cabinet minister turned vehement Kremlin critic.
Hundreds of opposition supporters -- responding to a call on the Internet -- tried to attend the rally. But they were vastly outnumbered by members of pro-Kremlin youth who noisily beat drums to show their support of United Russia.
Oleg Orlov, the head of the Memorial human rights centre who took part in the rally, told AFP: "Police are behaving in a rough, rude manner, pushing people."
In Russia's second city of Saint Petersburg, around 300 opposition supporters tried to stage a rally on the main Nevsky Prospekt avenue, shouting "shame!". But around 50 people were arrested, an AFP correspondent reported.
Interior ministry spokesman Oleg Yelnikov told AFP the security forces were on a "heightened regime" of alert, adding that some 11,500 interior ministry troops would ensure order nationwide.
Police said they arrested 300 people including prominent activist Ilya Yashin and opposition blogger Alexei Navalny in Monday's protest. A Moscow court on Tuesday found both men guilty of disobeying police orders, handing them a 15-day jail sentence.
Throughout the morning, Russian bloggers posted videos and claimed they saw columns of armoured vans carrying troops heading down the main avenues into the city.
An AFP correspondent saw around 20 vehicles and 15 buses, some empty, some filled with police in central Moscow.
Moscow police warned they would prevent any unsanctioned protests in the Russian capital and participants would be arrested.
Meanwhile Putin played down the sharp election losses as an inevitable outcome of tough economic times. "There were losses, but they were inevitable... Under the present circumstances, this is a good result," he said.
"We are not simply adapting, we are responding to the challenges of time, always and in everything. And yours truly too, I hope," he said in a televised meeting with supporters.
The opposition and many ordinary Russians have taken to calling United Russia the party of "swindlers and thieves" after a phrase first coined by Navalny.
Putin told his supporters not to pay attention, saying authorities have always had to struggle with "cliches".
The ruling party polled less than 50 percent of the vote, down from over 64 percent in 2007. It took 238 seats in the 450-seat State Duma, down sharply from the 315 seats it won in the last elections in 2007.
United Russia's biggest opposition will be the Communist Party with 92 seats.