Outgoing Dutch Prime Minister Mark Rutte, the front-runner to be the next secretary-general of NATO, said Saturday that Europe should stop whining about Donald Trump and focus instead on what it could do for Ukraine.

Former President Trump has sparked outrage in Europe, boasting in the past he would not defend NATO allies who fail to spend enough on defense.

"We should stop moaning and whining and nagging about Trump," Rutte told the Munich Security Conference.

He added: "It's up to the Americans. I'm not an American, I cannot vote in the U.S. We have to work with whoever is on the dance floor."

He said Europe should in any case be spending more on defense and ramping up ammunitions production, not just because Trump might come back.

He said Europe needed to increase its support for Ukraine because it was in its interests.

Rutte, who unexpectedly announced his departure from Dutch politics in July, has said he does not know if he is being considered a front-runner to lead NATO and would not start a personal campaign.

"And all that whining and moaning about Trump. I hear that constantly over the last couple of days. Let's stop doing that," Rutte said, adding that after talking with U.S. politicians in Munich he was "cautiously optimistic" that a U.S. military aid package that has stalled would eventually pass.

NATO Secretary-General Jens Stoltenberg has been in post since 2014 and is due to step down in October 2024.

His term was extended in July for a fourth time, as the alliance's 31 members opted to stick with an experienced leader rather than try to agree on a successor with Russia's war in Ukraine raging on NATO's doorstep.

Before NATO decided to stick with Stoltenberg, diplomats said Rutte would have been a strong candidate to succeed him, but the Dutchman had insisted he was not available at that time.