The web site of the Russian Embassy in London was brought down by a suspected distributed denial of service attack, according to a statement put out by the embassy.
The embassy thinks it was attacked ahead of Prime Minister David Cameron's visit to Russia and is blaming UK hackers objecting to closer ties with the country for the outage.
The visit is the first by a British leader to Moscow since the 2006 killing in London of Kremlin dissident Alexander Litvinenko, whose murderwith a dose of polonium-210 outraged British authorities.
"Prior to the visit of Prime Minister David Cameron to Russia, the website of the Russian Embassy in London (www.rusemb.org.uk) was brought down by a suspected DDoS (distributed denial of service) attack," the embassy statement said.
The embassy has set up a mirror web site providing information on Cameron's trip to Russia which began yesterday.