President Trump has claimed it would be an honour to meet Kim Jong-un if he was invited
Mr McCain’s comments come after the incumbent US President last week revealed he would be “honoured” to meet Kim Jong-un if he was invited to visit North Korea.
The shock claim came just a day after the President had praised the North Korean dictator as a “pretty smart cookie”.
But fellow Republican Mr McCain, who ran against Barack Obama for the presidency in 2008, said: ”I don't understand it and I don't think that the President appreciates the fact that when he says things like that it helps the credibility and the prestige of this really outrageous strongman.
President Trump described Kim Jong-un as a 'pretty smart cookie'
“It's very disturbing. It's disturbing because we are proud Republicans and we stand for human rights, the reason the United States of America was called the shining city on the hill.”
“I wish that the President would consider much more carefully his comments, particularly in praise of a North Korean — he's worse than a dictator. He's a despot. He’s — I've run out of adjectives and adverbs.”
The Republican added: ”The largest gulag left on earth is in North Korea. And we all know about their human rights abuses and others.
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I don't think that the President appreciates the fact that when he says things like that it helps the credibility and the prestige of this really outrageous strongman
Senator John McCain
“We have to stand for those fundamental principles so that we can assume a leadership role in the world.”
The Arizona senator warned that action may need to be taken if Pyongyang is capable of mounting a nuclear weapon onto a ballistic missile.
But remaining cautious, Mr McCain, who chairs the Senate Armed Services Committee, added that a strike against the rogue state should be a last resort.
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Speaking about President Trump Mr McCain continued: “About half the time, I agree with him, because one day it's one comment and then the next day another.
“Consistency has got to be the fundamental pillar of the conduct of national security policy.”
Mr Trump’s recent comments has sparked concern among his fellow Republicans and former rival Hillary Clinton, who has also accused President Trump of having a “Twitter foreign policy”.
The Democrat said: "Negotiations are critical, but they have to be part of a broader strategy, not just thrown up on a tweet some morning that, 'Hey let's get together and, you know, see if we can get along and maybe we can come up with some sort of a deal.' That doesn't work.
Her sentiments were echoed by Republican senator for South Carolina, Lindsey Graham, who warned that a meeting with Kim Jong-un would only “empower” the dictator.