EU leaders of the bloc's 27 states gather for talks with Ukrainian President Volodymyr Zelensky and aim to cement support for the war-torn country amid US President Donald Trump's freeze on military aid to Kyiv.

In a speech on Wednesday, President Emmanuel Macron announced he would discuss extending France's nuclear deterrent to other European nations.

"This readiness of France, this is something very promising," Polish Prime Minister Donald Tusk told reporters in Brussels, adding: "We have to treat this proposal seriously."

He also reiterated a call for Europe to strengthen its defences against Russia.

"It must be one of our priorities to coordinate all our capacities in Europe and to build, in fact, one well-coordinated military power. This is what can give us a clear advantage towards Russia," Tusk said.

"Europe must take up this challenge, this arms race, and it must win it," he added.

Poland, a NATO member and a key ally of its neighbour Ukraine, also shares a border with Russian exclave of Kaliningrad, and Belarus, Moscow's ally.

Macron said he would open a debate on extending France's nuclear deterrent to other European nations, following a "historic" call from likely next German chancellor Friedrich Merz on extending that umbrella of protection.

Merz, whose right-wing party won the Germany elections, said last month he wanted a discussion on "nuclear sharing" with France and Britain, Europe's only nuclear powers other than Russia.

In April, Poland's President Andrzej Duda said his country was ready to host NATO's nuclear arms.

Moscow in response warned it would take steps to "ensure its security".