"er-region.ru is down!" the LegionRussia Twitter account said.
The hackers justified the attack on the site in another message on Twitter, saying the site's content was "nauseating" in its praise of party leader Vladimir Putin.
A third message from the account estimated the cost of the server that hosted the party's site at 350,000 rubles ($12,000) and said "They think that they can pay for everything from the budget. Have to punish them."
Anonymous took credit for the recent leak of emails from Federal Youth Agency chief Vasily Yakemenko and his spokeswoman Kristina Potupchik. Among the emails was correspondence with Potupchik that contains a suggestion of initiating DDoS attacks on the website of newspaper Kommersant. The newspaper suffered a DDoS attack just days after the date of Potupchik's leaked email.