McCain, chairman of the Senate Armed Services Committee, has scheduled a hearing for Thursday on foreign cyber threats.
"When you attack a country, it's an act of war," McCain said in an interview with the Ukrainian TV channel "1+1" while on a visit to Kiev, according to Reuters.
"And so we have to make sure that there is a price to pay, so that we can perhaps persuade the Russians to stop these kind of attacks on our very fundamentals of democracy."
President-elect Donald Trump praised Russian President Vladimir Putin on Friday for refraining from retaliation after the United States expelled 35 Russian diplomats.