The US government has formally accused Russia of conducting cyber attacks against American political organisations during the campaign for the November 8 presidential election, including hacking of Democratic Party emails.
Friday's statement was the first official accusation by American officials against Russia in the spate of cyber attacks.
"We believe, based on the scope and sensitivity of these efforts, that only Russia's senior-most officials could have authorised these activities," said a joint statement from the Department of Homeland Security and Office of the Director of National Intelligence.
The statement said the US intelligence community "is confident that the Russian government directed the recent compromises of e-mails from US persons and institutions, including from US political organisations".
It said the disclosures of alleged hacked emails disclosed on WikiLeaks and other websites and by the online persona "Guccifer 2.0" were "consistent with the methods and motivations of Russian-directed efforts."
"These thefts and disclosures are intended to interfere with the US election process," the statement said.
"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."
The statement, however, stopped short of accusing Russia in the recent cyber attacks on state election databases.
"Some states have also recently seen scanning and probing of their election-related systems, which in most cases originated from servers operated by a Russian company," the statement said.
"However, we are not now in a position to attribute this activity to the Russian government."
The condemnation coincides with increasing tensions between the US and Russia on a range of international issues, from the Middle East to Ukraine and cyberspace.