“Any suggestion that allies will not defend each other undermines all of our security, including that of the US, and puts American and European soldiers at increased risk”, said NATO Secretary General Jens Stoltenberg in a written statement.

“Any attack on NATO will be met with a united and forceful response,” he added, reacting to remarks on Saturday by Trump, who is likely to be the Republican nominee in this year’s US presidential election.

Polish Defence Minister Wladyslaw Kosiniak-Kamysz also weighed in.

“NATO’s motto ‘one for all, all for one’ is a concrete commitment. Undermining the credibility of allied countries means weakening the entire NATO,” he wrote on social media platform X.

“No election campaign is an excuse for playing with the security of the Alliance.”

Germany’s foreign ministry posted the message ‘One for all and all for one’ with the hashtag #StrongerTogether on its English language X account following Trump’s comments.

EU Council President Charles Michel said: “Reckless statements on #NATO’s security and Art 5 solidarity serve only (Russian President Vladimir) Putin’s interest.”

Article 5 of the NATO treaty says that an armed attack against an alliance member will be considered an attack against them all, triggering collective self-defence.

Trump, speaking during a political rally in South Carolina and appearing to recount a meeting with NATO leaders, quoted the president of “a big country” that he did not name as asking, “Well sir, if we don’t pay, and we’re attacked by Russia – will you protect us?”

“I said: ‘You didn’t pay? You’re delinquent?’ He said: ‘Yes, let’s say that happened.’ No I would not protect you. In fact I would encourage them to do whatever the hell they want. You gotta pay.”

“We have heard that before … Nothing new under the sun”, said EU Internal Market Commissioner Thierry Bretonin an interview with France’s LCI television, adding:

“He maybe has issues with his memory, it was actually a female president, not of a country, but of the European Union,” Breton said, referring to European Commission President Ursula Von der Leyen and a conversation she had with Trump in 2020.

“We cannot flip a coin about our security every four years depending on this or that election, namely the US presidential election,” Breton said, adding European Union leaders understood the bloc needed to boost its own military spending and capacities.

White House spokesperson Andrew Bates, asked about Trump’s comments, 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.”

NATO’s 31 members have agreed on a target of spending at least 2% of gross domestic product on defence, but NATO estimates have shown that only 11 are spending that much.

(Reporting by Tassilo Hummel, Victoria Waldersee, Sabine Siebold and Foo Yun Chee, Additional reporting by Anna Wlodarczak-Semczuk; Editing by Frances Kerry and Giles Elgood)