US senator John McCain: Putin greater threat than Isis

Veteran US senator John McCain, in Australia for talks on security in the Indo- Pacific region, admits President Donald Trump makes him nervous "from time to time".

He also believes Russian leader Vladimir Putin is a greater threat than the terrorist group ISIS.

"I have taken the practice of not reacting to what the president says but what the president does," Senator McCain told ABC TV.

He cited the US military response to the gassing of hundreds of civilians by the Bashar regime in Syria. The senator believes Trump has the confidence of his national security team, and, most of the time, accepted their advice.

"Can I tell you that he does [that] all the time? No. Does it bother me? Yes, it bothers me," he said.

Senator McCain warned Russia was trying to influence elections around the world, even though he'd seen no evidence they succeeded.

"I view Vladimir Putin - who has dismembered Ukraine, a sovereign nation, who is putting pressure on the Baltics - I view the Russians as the far greatest challenge that we have."

Senator McCain also called for US allies to assist in challenging Chinese assertions of sovereignty in the South China Sea.

"So we may be asking our allies and friends to make a larger contribution once we have and it will be soon, once we have announced a strategy for victory," he told The Australian.

Senator McCain is also expected to underline the importance of Australia's historic ties with the US during a major foreign policy speech in Sydney today.

- AAP