The U.S. government has condemned the mass arrest of protesters at anti-corruption demonstrations across Russia on Sunday.
The protests, coordinated by Russian opposition leader Alexei Navalny, drew crowds of more than 8,000 in Moscow and more than 10,000 in St. Petersburg.
Anti-corruption rallies were held in more than 80 towns and cities across Russia, making the protest one of the largest in Russia for more than five years.
In a number of cities, including Moscow, demonstrators gathered even though the anti-corruption events had not been sanctioned by local authorities.
Russian human rights group OVD-Info said that around 1400 demonstrators were detained across the country, with more than 1,000 held by police in the capital.
Among those detained were several journalists, including a reporter for the UK's Guardian newspaper, Alec Luhn.
Navalny was detained by police shortly after the rally began in Moscow. He is expected to appear at the capital's Tverskoy court later on Monday.
"The United States strongly condemns the detention of hundreds of peaceful protesters throughout Russia on Sunday," acting State Department spokesperson Mark Toner said in a statement on Sunday.
"We were troubled to hear of the arrest of opposition figure Alexei Navalny upon arrival at the demonstration, as well as the police raids on the anti-corruption organization he heads."
Toner said, "Detaining peaceful protesters, human rights observers, and journalists is an affront to core democratic values."
The European Union also criticized the arrests, which they said violated the Russian constitution.
"Police operations in the Russian Federation, attempting to disperse demonstrations and detaining hundreds of citizens, including opposition leader Alexey Navalny, prevented the exercise of basic freedoms of expression, association, and peaceful assembly - which are fundamental rights enshrined in the Russian constitution," an EU spokesperson said in a statement.
"We call on the Russian authorities to abide fully by the international commitments it has made and to release without delay the peaceful demonstrators that have been detained."
Navalny, who is set to run in Russia's 2018 presidential elections, called for mass demonstrations after accusing Prime Minister Dmitry Medvedev of heading a multi-billion-dollar corruption scheme.
Russia's Anti-Corruption Foundation, an NGO created by Navalny in 2011, accused Medvedev in this month of collecting bribes through charitable organizations run by close friends and former classmates.
The organization claimed that Medvedev owns four mansions across the country, worth several million dollars each. Other alleged holdings include two large plots of land in Krasnodar, an Italian vineyard, and a lavish residential building in the heart of St. Petersburg with luxurious apartments and two yachts.
The Kremlin has refused to comment on the claims.