Russia's Internet watchdog said about 4,500 websites were blocked in the country last year because of alleged extremist content, the Interfax news agency reported.
Agency specialists identified 3,500 violations of Russia's extremism laws, and prosecutors informed them of another 700, Roskomnadzor head Alexander Zharov was cited as saying Tuesday by Interfax.
The watchdog has been acting under new legislation signed into law in December 2013 by President Vladimir Putin that allows websites to be blocked without authorization from a court.
Critics say the law has been used to stifle political dissent, with the blog of opposition leader Alexei Navalny and Kremlin-hostile news website Grani.ru among the online platforms that have been blocked since the law came into force in February.
Most of the restrictions on accessing websites were subsequently lifted after their owners removed the offending material, Zharov was cited as saying.