The US has accused Russia of hacking political websites, claiming the country is trying to interfere with the upcoming presidential election in America.
Intelligence officials said they are confident that the Russian government directed the recent breaches of emails from American people and institutions, including US political organisations.
The Office of the Director of National Intelligence and the Department of Homeland Security in America have released a joint statement saying that based on the "scope and sensitivity" of the hacking efforts, only Russia's "senior-most officials" could have authorised these activities.
Pressure has been mounting on the Obama administration to confront Russia over the hacking of political groups, including the Democratic National Committee.
The White House declined to say whether the formal attribution would trigger sanctions against Russia.
A senior Obama administration official said the US would respond "at a time and place of our choosing", but any retaliation may not take place in the open.
The official said the public will not necessarily know what actions the US has already taken or will take in the future against Russia in cyberspace.
US f ederal officials are investigating cyber attacks at the Democratic National Committee and the Democratic Congressional Campaign Committee.
Election data systems in at least two states also have been breached.
"We believe, based on the scope and sensitivity of these efforts, that only Russia's senior-most officials could have authorised these activities," the Office of the Director of National Intelligence said in a joint statement with the Department of Homeland Security.
The statement said recent disclosures of alleged hacked emails on websites like DCLeaks.com and WikiLeaks, and by the Guccifer 2.0 online persona, are consistent with the methods and motivations of efforts directed by Russia - which has denied any involvement.
The statement continued: "These thefts and disclosures are intended to interfere with the US election process.
"Such activity is not new to Moscow. The Russians have used similar tactics and techniques across Europe and Eurasia, for example, to influence public opinion there."
California representative Adam Schiff, the ranking member of the House intelligence committee, applauded the administration's decision to publicly name Russia as the source of the hacking.
He said: "We should now work with our European allies who have been the victim of similar and even more malicious cyber interference by Russia to develop a concerted response that protects our institutions and deters further meddling."
Intelligence officials say some states have experienced scanning or probing of their election systems, which in most cases originated from servers operated by a Russian company.
They stopped short, though, of attributing this activity to the Russian government. And US government officials say it would be difficult to alter the results of the forthcoming election because of the decentralised nature of the American electoral process.