Russian police have detained about 40 people, including four prominent opposition figures, in efforts to break up an unsanctioned anti-government rally in Moscow.
Opposition leaders Alexei Navalny, Sergei Udaltsov, Ilya Yashin and Ksenia Sobchak were among those detained Saturday.
The protest was organized to commemorate a year of rallies against President Vladimir Putin and his rising influence.
Thousands of people gathered for the demonstration despite freezing cold temperatures and a heavy police presence in Moscow's Lubyanka Square near the headquarters of Russia's Federal Security Service.
Moscow city officials had denied a permit for the rally.
Navalny, a major organizer of anti-Kremlin protests, is under investigation by Russian authorities for suspected fraud and money laundering. He has denied the charges, which carry a 10-year prison sentence.
Also Saturday, opposition groups created a new party called The People's Alliance, in an attempt to galvanize critics of Russia's government.
Lubyanka Square is home to the Solovetsky Stone, a monument to victims of political repression during the Soviet era. Many protesters brought flowers to place on the stone in tribute to those victims.
President Putin has held the top two spots in Russian government — president and prime minister — for more than a decade, swapping the top posts with his hand-picked successor, Dmitry Medvedev. Mr. Putin won a third presidential term earlier this year. Russia's parliament has since passed laws cracking down on freedom of speech and freedom of assembly.
Russian authorities say Navalny is being investigated for the alleged theft of $1.8 million from one of his companies.
Authorities already have another financial case open against Navalny. Investigators said earlier this year they suspect he played a part in a scheme to steal assets from a state timber company — totaling about $500,000 — while he was advising a local governor in 2009.