"We should not undermine the credibility of NATO's deterrence," Jens Stoltenberg said on Wednesday, issuing a public rebuke to Donald Trump, APA reports citing Euronews.
"Deterrence is in the mind of our adversaries. We should not leave (any) room of miscalculation or misunderstanding in Moscow about our readiness, our commitment and our resolve to protect all allies," the Secretary General said on Wednesday ahead of a meeting in Brussels of the alliance's defence ministers.
"And the reason to do so is not to provoke a conflict but to prevent a conflict as NATO has done successfully for the 65 years."
Keeping NATO strong is in "the national interest of the United States," he added, as the country "has never fought a war alone."
Stoltenberg's caveat comes days after Trump, who is running again for president and is currently the Republican frontrunner, suggested in a South Carolina rally he would "encourage" Russia to attack any NATO nation that does not meet the target of spending 2% of gross domestic product (GDP) on defence.
"The whole idea of NATO is that an attack on one ally will trigger a response from the whole alliance. As long as we stand behind that message, together, we prevent a military attack on any ally. So the purpose of NATO is to prevent war, to preserve peace," Stoltenberg told reporters when asked about Trump's comments.
"So any suggestion that we're not standing up for each other, that we're not going to protect each other undermines the security of all of us, increasing the risks," he went on. "It's important that both in actions and in words we communicate clearly that we stand by NATO's commitment to protect and defend all allies."
First agreed in 2006, the pledge of NATO allies to spend 2% of their GDP on defence is a shared objective, rather than a legally binding obligation.
The target has been reaffirmed several times over the years and became a minimum requirement in the wake of Russia's all-out war in Ukraine. European governments have since then announced national plans to rapidly ramp up their defence spending, although as of 2023, only 11 of the 31 allies met the 2% target.
On Wednesday, Stoltenberg revealed that, according to the alliance's latest estimates, up to 18 allies will reach the objective by the end of 2024. European allies and Canada are expected to invest $380 billion in defence.