With the continent looking to rearm following Russia's invasion of Ukraine and US President Donald Trump's stance on European security, the European Commission last month said it would give member states more wiggle room on spending.

In an easing of its once strict rule on budget deficits, Brussels will now let states splash out up to 1.5 percent of national output on defence for four years without fear of breaching its strict public debt limits.

Belgium, Bulgaria, the Czech Republic, Denmark, Germany, Estonia, Greece, Croatia, Latvia, Lithuania, Hungary, Poland, Portugal, Slovenia, Slovakia and Finland have decided to trigger the budget exemption clause, an EU statement said.

EU countries had until the end of April to inform the bloc of their decision to opt in to the suspension.

Twelve countries had already formally requested exemption and four more had committed to do so, according to the European Commission and European Council.

In March, the EU forecast that the suspension could unlock defence spending worth up to 650 billion euros ($736 billion), while acknowledging that figure was an estimate.

France, Spain and Italy have been among countries to stay away from the exemption, even though they have pledged to increase their defence spending.

"We remain open for more requests" for exemptions, European Economic Affairs Commissioner Valdis Dombrovskis said on Wednesday, quoted in a press release.

Since 2021 military spending by the 27 EU members has risen by more than 31 percent, reaching 326 billion euros in 2024.