The United States has expelled 35 Russian diplomats and closed two Russian compounds in a response that Barack Obama says was "necessary and appropriate" against "efforts to harm US interests".
The United States president, whose term ends in January next month, said actions against Russia are "a necessary and appropriate response to efforts to harm US interests in violation of established international norms of behaviour".
Obama said the Department of Homeland Security and Federal Bureau of Investigation are releasing declassified technical information on Russian civilian and military intelligence service cyber activity.
He said all the Americans should be alarmed by Russia's actions, adding that data theft and disclosure activities could only have been directed by the highest levels of the Russian government.
Earlier in the day, a senior US official told Reuters news agency that the Russian diplomats would be given 72 hours to leave the United States.
Access to the two compounds located in New York and Maryland will be denied to all Russian officials as of noon on Friday, the official added.
Obama said the United States diplomats have experienced an unacceptable level of harassment in Moscow by Russian security services and police over the last year.
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