Europe is “dreaming” if it believes it can defend itself without US backing, Nato’s secretary-general has warned, pushing back against calls in some EU capitals to prepare for a future without Washington’s protection.

The comments come after Donald Trump threatened to use military force to seize Greenland from Nato ally Denmark and to impose tariffs on other allies who opposed him — remarks that unsettled European governments and reignited debate over the continent’s reliance on the US. Although the US president rescinded the threats last week, they prompted renewed calls for Europe to accelerate efforts to strengthen its own defence capabilities.

Mark Rutte, Nato’s secretary-general who last week persuaded Trump to withdraw his threats, dismissed those arguments on Monday. Rutte told EU lawmakers that building a fully independent European defence would be prohibitively expensive and would benefit only the bloc’s adversaries, including Russian President Vladimir Putin.

“If anyone thinks here . . . that the European Union or Europe as a whole can defend itself without the US, keep on dreaming,” he said in remarks to the European parliament. “You can’t.”

“I think there will be a lot of duplication and I wish you luck if you want to do it, because you have to find the men and women in uniform . . . on top of what is happening already,” he said. “It will make things more complicated. I think Putin will love it. So think again.”

Independence from the US security umbrella that has shielded Europe since the second world war was once a niche idea, promoted largely by France.

But the notion of “strategic autonomy” has moved steadily into the EU mainstream in recent years, as Donald Trump’s erratic approach to Nato allies — reinforced by Russia’s 2022 invasion of Ukraine — has sharpened debate over how Europe can strengthen its own defence capabilities.

Last year Nato allies agreed to lift their defence spending to 5 per cent of GDP by 2035, responding to Trump’s demand that Europe shoulder a larger share of the burden for its own defence.

Even so, experts warn that fully replacing the US role in Europe — particularly in areas such as advanced weaponry and critical capabilities on which European forces have relied for decades — would be vastly more expensive.

“If you really want to go it alone, forget that you can ever get there with 5 per cent [defence spending]. It will be 10 per cent,” Rutte said on Monday. “You have to build up your own nuclear capability. That costs billions and billions of euros.”