President Barack Obama has sanctioned Russian intelligence services and their top officials, kicked out 35 Russian officials and closed down two Russian-owned compounds in the US in a sweeping response to election hacking.
It was the strongest action the Obama administration has taken to date to retaliate for a cyber attack.
"All Americans should be alarmed by Russia's actions," Mr Obama said in a statement released while he was on holiday in Hawaii.
He added: "Such activities have consequences."
Mr Obama ordered sanctions against two Russian intelligence services, the GRU and the FSB, plus companies which the US says support the GRU.