As well as rearmament, leaders are expected to discuss how the body can further support Kyiv in the face of US President Donald Trump's announcement on Monday that he would suspend aid to Ukraine. Ukrainian President Volodymyr Zelensky is invited to the summit.

Nerves have grown increasingly frayed across Europe since Trump and Zelensky's showdown at the White House last week, and the rhetoric around Thursday's summit leaves no doubt about the importance EU officials are ascribing to it.

Three years on since Russia's full-scale invasion of Ukraine, the Trump administration's overtures to Russian President Vladimir Putin have left many in Europe concerned the continent would not be able to rely on US support for its security.

Washington's decision on Wednesday to pause intelligence sharing with Ukraine did nothing to allay those worries.

In a sign of the depth of concern, President Macron said France was open to discussing extending the protection offered by its nuclear arsenal to its European partners, during an address to the nation on Wednesday.

That followed a call from Friedrich Merz, likely to be Germany's next chancellor, to discuss increased nuclear sharing.