Russian President Dmitry Medvedev's blog has fallen victim to a cyber attack on a hosting website which is popular with government critics who say the attack may herald a clampdown on freedom of speech.

Medvedev's blog at http://community.livejournal.com/blog_medvedev was down for at least an hour on Wednesday, before service was restored. A Kremlin official who declined to be identified confirmed the shutdown was due to a cyber attack.

Livejournal hosts more than 4.7 million Russian bloggers who exchange information and share critical views which cannot be expressed in the mainstream media. Many bloggers carry out their own investigations into crimes by officials.

Possibly, we are witnessing a field exercise aimed at preventing public unrest during the State Duma elections in December and the presidential vote in March, opposition politician Vladimir Ryzhkov, also an active Livejournal blogger, said on his website www.ryzhkov.ru.

Internet services played a prominent role in popular uprisings in the Middle East, prompting some governments to shut down the Internet. Russian authorities are keen to avoid similar scenarios in the run up to the election for the lower house of Russia's parliament.

Denial of service attacks on Livejournal -- a simple, but effective way to disrupt a website by swamping it with outside requests or messages -- started as early as March 24, Alexander Gostev, anti-virus expert at Kaspersky Labs said.

He said the first site to come under attack was a blog of Russian anti-corruption activist Alexei Navalny on March 24.

On April 4, the same botnet, a collection of software agents which run the malicious software, received cyber commands to attack other popular Russian blogs, among them Medvedev's, he said.

Possibly, by expanding the number of targets for their attacks, the masterminds are trying to hide the original purpose of their illegal acts, he said.

Ilya Dronov, an executive at SUP, a company which runs Livejournal, said in a statement that the attacks were aimed at destroying the site. Gostev said finding those responsible would require a large-scale international police operation.

(Writing by Alexei Anishchuk; Editing by Michael Roddy)

Russia Dmitry Medvedev Down