"No," McCain said when asked if there was any indication of imminent military action against the North during Wednesday's White House briefing. "But it is clear and I totally agree that that option can't be taken off the table, but it has to be the absolute last option," he said.

"When I say last option, that is when we're convinced that North Korea has that capability to launch a missile that could strike with a nuclear weapon the west coast of the United States," he said, adding that North Korean leader Kim Jong-un "is not a person that we can depend on to act in a rational fashion."

McCain also said a "red line" could be when a nuclear-tipped missile is on the launch pad.

"I don't think we could wait till launch. We do have defensive capabilities that can intercept missiles, but to count on that alone I think would be very risky business," he said.

McCain also warned that military action could result in North Korean retaliatory strikes that can devastate Seoul.

"That's why a lot of the emphasis has got to be on the only power that can restrain them and that's China," he said. "The Chinese cut back on coal supplies, but I was not encouraged when the Chinese came against our air defense system being emplaced in South Korea. The Chinese have to really be made aware that this could have a profound effect on our relations with China."

He was referring to Beijing's opposition to the deployment of the US THAAD missile defense system in the South. China has long claimed the system could be used against it despite repeated assurances that it is a purely defensive system designed only to counter North Korean threats. (Yonhap)