While Europe's military heavyweights have already said that meeting President Donald Trump's potential challenge to spend up to 5% of their economic output on security won't be easy, it would be an especially tall order for Spain.

The leader of Germany's conservative CDU, the party's candidate to run for chancellor, said on Tuesday that the nation should focus on efforts to reach existing NATO defence spending targets before discussing any further increases.

Germany met NATO's target to spend 2% of its gross domestic product on defence in 2024, the government said on Monday, though well short of incoming U.S. President Donald Trump's call for as much as 5%.