In a joint statement Friday, the Department of Homeland Security and the Office of the Director of National Intelligence on Election Security said that U.S. intelligence is “confident that the Russian government directed the recent compromises of emails from US persons and institutions, including from U.S. political organizations” and that “only Russia’s senior-most officials could have authorized these activities.”

The confirmation follows months of widespread belief that Russian state actors were responsible for a major hack of emails from the Democratic National Committee. The fruits of that attack were distributed via channels including Wikileaks.

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Among other consequences, the leaked emails led to turmoil among U.S. progressives over the DNC’s perceived unfair treatment of former primary candidate Bernie Sanders. Though that rift does not seem to have had a lasting impact on former Sanders supporters’ willingness to vote for now-Democratic Nominee Hillary Clinton, it illustrates the potential of such tactics to manipulate election outcomes.

The new statement debunks claims by a persona known as “Guccifer 2.0” to have been the unaffiliated lone operator responsible for the hack. At the same time, the statement said that attacks on U.S. election systems, though in many cases originating from Russian servers, could not yet be attributed to the Kremlin. Officials also say that it would be “extremely difficult” even for a well-resourced state actor to interfere directly with election results.

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A spokesman for Vladimir Putin quoted by the Guardian called the claims “rubbish,” claiming that Russian government websites were regularly targeted by “a lot” of attacks traced to the U.S., “but we do not blame the White House or Langley each time.”