The meeting in Brussels could become a decisive moment for European security.
EU leaders are gathering in Brussels for a special defence council as French President Emmanuel Macron warns the continent is at a "turning point in history".
As well as rearmament, leaders are expected to discuss how they can continue to support Kiev amid US President Donald Trump's announcement on Monday that he would suspend aid to Ukraine. Ukrainian President Volodymyr Zelensky has been invited to the summit.
Following Trump and Zelensky's meeting at the White House last week, nerves in Europe are increasingly tense, and the rhetoric surrounding the summit today leaves little doubt about the importance EU officials attach to it, says a BBC analysis.
Three years after Russia's full-scale invasion of Ukraine, the Trump administration's overtures to Russian President Vladimir Putin have led many in Europe to fear that the continent will not be able to rely on US support for its security.
Washington's decision on Wednesday to suspend intelligence sharing with Ukraine did nothing to allay those concerns.
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 last night.
That followed a call by Friedrich Merz, who is likely to be Germany's next chancellor, to discuss greater nuclear exchanges.
Europe faces "a clear and present danger on a scale none of us has seen in our lifetime", European Commission head Ursula von der Leyen said, while European Council President António Costa said it was "a decisive moment for Ukraine and European security".
In a letter to European leaders, von der Leyen also said the continent must "seize the moment" and "deploy our industrial and productive power and direct it towards the goal of security."
On Monday, von der Leyen announced an unprecedented defence package - dubbed ReArm Europe - and said Europe was ready to "massively" increase its defence spending "with the necessary speed and ambition".
Von der Leyen said the three proposals outlined in the ReArm Europe plan would both support Ukraine and "respond to the long-term need to take much greater responsibility" for European security - presumably given the fact that many Europeans believe the continent can no longer automatically rely on the US to come to its aid.
Proposals include:
- Allowing countries to increase their national deficit levels to allow for greater defence spending.
- €150bn (£125bn) in loans for defence investment in areas that could benefit EU defence as a whole - such as air and missile defence, anti-drone systems and military mobility - helping to pool demand and reduce costs through joint procurement
- Allowing countries to redirect funds earmarked for cohesion policy programmes (policies aimed at closing the gap between more and less favoured regions) towards defence spending.
The European Investment Bank will also be able to finance military projects.
According to von der Leyen, the plan could free up a total of €800 billion ($860 billion; £670 billion) for defence spending.
Many European leaders have expressed their support for swift and decisive action on the continent's security.
Polish Prime Minister Donald Tusk said the Commission's plan represented a "fundamental change", while Lithuanian President Gitanas Nauseda said the summit would give Europe an opportunity to show "whether it is just a debating club or whether we can take decisions".
But dissent is expected from some European leaders sympathetic to Moscow.
Earlier this week, Slovak Prime Minister Robert Fico said the EU's "peace through strength" approach was "unrealistic".
And in a letter to Costa, Hungarian Prime Minister Viktor Orban asked that Ukraine not be mentioned in the written conclusions after the summit.
Orban - who has repeatedly tried to block EU aid to Ukraine and praised Trump for "courageously defending peace" - said there was now a "strategic divide... between most of Europe and the US".
"One side is pushing for a prolongation of the war in Ukraine, while the other is seeking an end to the conflict," he added.
However, Orban left the door open to "greater likelihood of cooperation" with other leaders on common security and defence issues.
While the crisis summit takes place in Brussels today, UK defence secretary John Healey will be in Washington to discuss with his counterpart Pete Hegseth the US decision to suspend intelligence sharing with Ukraine.
Their bilateral meeting will focus on a possible peace plan as efforts continue to bridge the transatlantic rift over Kiev's future security.
Perhaps in a last-ditch effort to forge unity before the summit, Emmanuel Macron, who has put himself at the centre of EU efforts to bridge the gap between Kiev and Washington, invited Orban to dinner in Paris on Wednesday evening.
The two leaders met immediately after the French president made a sombre address to the nation in which he said France and Europe must be ready if the United States was no longer on their side.
"We must be united and determined to defend ourselves," Macron said. He added that Europe's future could not be tied to Washington or Moscow, and said that while he "wants to believe that the United States will remain on our side, we must be prepared for that not to happen."
The French president plans to hold a meeting of European army chiefs in Paris next week.
Macron said "decisive steps" will be taken in Brussels that will leave European countries "better prepared to defend and protect themselves."
"The moment requires unprecedented decisions," he concluded. I BGNES