"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 Kyiv, Mirror reported.
"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," he said.
Read alsoReuters: U.S. senators urge Trump to take tough line on Russia over Ukraine (Document)McCain, chairman of the Senate Armed Services Committee, has scheduled a hearing for Thursday on foreign cyber threats.
Yet President-elect Donald Trump praised Russian President Vladimir Putin on Friday for refraining from retaliation after the United States expelled 35 Russian diplomats.
And that came on the same day the FBI formally accused Russian agents of hacking during the US election campaign in an extraordinary report.
A 13-page dossier details how "Russian intelligence services actors" compromised a political party twice and information from its servers were leaked to the press.
It does not name names but comes after a vast cache of Democratic Party e-mails was published by Wikileaks during the election.
Read alsoNew sanctions, expulsion of diplomats "not the sum total" of response to Russia’s aggressive activities – ObamaThe report by the FBI and Department of Homeland Security (DHS) is the most detailed set of hacking allegations against Russia so far by the US government.
It was published Thursday night as an international row blew up over the US decision to expel 35 Russian diplomats and draw up new sanctions.
"These actions were taken to respond to Russian harassment of American diplomats," a US official said.
Russia has branded hacking accusations "absolutely groundless" as its UK embassy posted a Twitter meme calling Obama a 'lame duck'.
The report was published alongside a joint statement by the FBI, Department of Homeland Security and Director of National Intelligence.
Read alsoRussia hacks Vermont utility, showing risk to U.S. electrical grid security - WPThe statement said: "This activity by Russian intelligence services is part of a decade-long campaign of cyber-enabled operations directed at the U.S. Government and its citizens.
