Republican frontrunner Donald Trump has revealed that during his first term as US president, he warned Nato allies that he “would encourage” Russia “to do whatever the hell they want” to countries that are “delinquent”.

Speaking at a rally in South Carolina, Mr Trump recounted a story he had told before about an unidentified Nato member who confronted him over his threat not to defend members who failed to meet the trans-Atlantic alliance’s defence spending targets.

Mr Trump recounted that he had told the member that he would, in fact, “encourage” Russia to do as it wishes in that case.

“‘You didn’t pay? You’re delinquent?'” Mr Trump recounted himself saying.

“‘No, I would not protect you. In fact, I would encourage them to do whatever the hell they want. You gotta pay. You gotta pay your bills.'”

Nato allies agreed in 2014, after Russia annexed Ukraine’s Crimean Peninsula, to halt the spending cuts they had made after the Cold War and move towards spending 2% of their gross domestic profit on defence by 2024.

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The White House expressed concern about Mr Trump’s comments (Manuel Balce Ceneta/AP)

White House spokesman Andrew Bates expressed concern about Mr Trump’s claims.

He said: “Encouraging invasions of our closest allies by murderous regimes is appalling and unhinged – and it endangers American national security, global stability, and our economy at home.”

The former US president’s comments come as Ukraine remains mired in its efforts to stave off Russia’s 2022 invasion and as Republicans in Congress have become increasingly sceptical of providing additional aid money to the country.

Earlier on Saturday, Mr Trump called for the end of foreign aid, arguing that the US should dramatically curtail the way it provides money.

Mr Trump wrote on his social media network in all-caps letters: “FROM THIS POINT FORWARD, ARE YOU LISTENING US SENATE(?), NO MONEY IN THE FORM OF FOREIGN AID SHOULD BE GIVEN TO ANY COUNTRY UNLESS IT IS DONE AS A LOAN, NOT JUST A GIVEAWAY.”

Mr Trump added the money could be loaned “ON EXTRAORDINARILY GOOD TERMS”, with no interest and no date for repayment.

But he said: “IF THE COUNTRY WE ARE HELPING EVER TURNS AGAINST US, OR STRIKES IT RICH SOMETIME IN THE FUTURE, THE LOAN WILL BE PAID OFF AND THE MONEY RETURNED TO THE UNITED STATES”.