The editorial staff at online newspaper Fontaka.ru told state news agency RIA Novosti from St. Petersburg that its website was the target of a distributed denial-of-service attack.
"There has been a DDoS attack going since morning," the editors said. "This is a very serious attack."
News services Novaya Gazeta and Ekho Moskvy reported similar attacks, as did online television network Dozhd. RIA Novosti reported that several Internet users across the country had intermittent problems Thursday.
A group describing itself as a "patriotic" network from hacking community Little Hamsters posted an online video taking responsibility for the attacks, though RIA Novosti said it wasn't able to verify the claim.
May 9 is the anniversary of the 1945 victory of Soviet forces over Nazi Germany. The anniversary has gained importance since President Vladimir Putin came to power in 2000. He's been more critical of his opponents since securing a third non-consecutive term as president last year.
U.S. lawmakers introduced legislation this week aimed at protecting national security interests from cyberattacks.