The Barack Obama administration on Thursday expelled 35 suspected Russian spies and imposed sanctions on two Russian intelligence agencies in retaliation to the Kremlin hacking into accounts of Democratic Party organisations and its candidates in the run up to the 2016 United States presidential elections. The US believes the breaches were orchestrated by Russian forces under the direct instructions of President Vladimir Putin, reported Reuters.

President Barack Obama, who is on vacation in Hawaii, said Russia’s actions should alarm all Americans. “These actions follow repeated private and public warnings that we have issued to the Russian government, and are a necessary and appropriate response to efforts to harm US interests in violation of established international norms of behaviour,” he said.

The Kremlin has promised adequate retaliation for the US’ actions. Moscow has also asked whether the new sanctions had the approval of the US President-elect Donald Trump, who has been a vocal supporter of Putin. Trump will take oath of office on January 20.

Russia has denied involvement in the hacking, which has led to the release of more than 20,000 emails and documents by WikiLeaks. The documents had revealed that top officials at the democratic committee had secretly planned to undermine Bernie Sanders’ presidential campaign during the Democratic primaries.

Trump, however, has repeatedly expressed scepticism that any such attack had taken place. “I don’t believe they [Russia] interfered,” he told TIME for its Person of the Year 2016 issue.