Hundreds of people have gathered in Moscow's Lubyanka Square for an anti-government rally, and at least one prominent Russian opposition figure has been arrested.

Leftist leader Sergei Udaltsov was detained Saturday as protesters marked one year since a series of demonstrations against the government of President Vladimir Putin began. The city of Moscow had denied a permit for the Saturday rally, but protesters gathered anyway.

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 ally, Dmitry Medvedev. Mr. Putin won a third term as president earlier this year. Since then, the Russian parliament has swiftly passed a raft of laws cracking down on freedom of speech and freedom of assembly, and designating some international nongovernmental organizations.

On Friday, Russian authorities launched a criminal investigation into prominent opposition activist Alexei Navalny for suspected fraud and money laundering.

Officials say Navalny is being investigated for the alleged theft of $1.8 million from one of his companies.

Russian 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.

Navalny has rejected the charges, which carry a 10-year prison sentence.