DONALD Trump would “encourage” Russia to attack any Western nations that fail to pay Nato defence bills.
The ex-US president bragged he once slapped down the leader of a “big country” who asked if America would step in if invaded by Russia.
Trump, running for president again, told supporters: “I said, ‘You didn’t pay? You’re delinquent? No I would not protect you’.
“In fact I would encourage them to do whatever they want. You gotta pay.”
A White House spokesman branded Saturday’s comments at a rally in South Carolina “appalling and unhinged” and a threat to global security.
Trump, 77, has claimed too much US cash is spent protecting 30 Nato nations and accused some of failing to spend enough on defence.
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He has also alarmed allies by claiming to have a working relationship with Russia leader Vladimir Putin while members of his party have blocked vital weapons cash for Ukraine.
Nato chief Jens Stoltenberg said: “Any suggestion that allies will not defend each other undermines all of our security.
“We expect that regardless of who wins the presidential election, the US will remain a strong and committed ally.”
Trump’s outburst came 24 hours after Russian drones blasted an oil depot in Kharkiv, killing seven.
Meanwhile, US warplanes blasted Houthi rebels in the latest mission to protect shipping in the Red Sea.