Russia and its president Vladimir Putin are a bigger threat to the world security than the Islamic State, U.S. Republican Senator John McCain has said.

"I think ISIS can do terrible things. But it's the Russians who tried to destroy the fundamental of democracy and that is to change the outcome of an American election," he said in an interview to the ABC channel.

"So I view Vladimir Putin — who has dismembered Ukraine, a sovereign nation, who is putting pressure on the Baltics — I view the Russians as the greatest challenge we face today," McCain added.