France is open to discussing an extension of its nuclear umbrella to its European partners, President Emmanuel Macron has said, as he warned that Russia was a threat for all of Europe.
France and the UK are Europe's only two nuclear powers.
In an address to the nation, Mr Macron also said that France would have to spend more on defence and would continue to help Ukraine.
He acknowledged voters' concerns over Russia and the new US government's upending of the international order.
"You are, I know, legitimately worried about the current events, which are disrupting the world order," Mr Macron said.
"Russia has become a threat for France and Europe," he said, adding that "to watch and do nothing would be madness."
European countries are scrambling to boost defence spending and maintain support for Ukraine after US President Donald Trump froze US military aid to Kyiv and fuelled doubts about the US's commitment to its European NATO allies.
Stressing that France was uniquely placed in Europe thanks to its nuclear deterrent capability, Mr Macron said he was open to discussing extending that protection to European allies.
He added that the ultimate decision on nuclear weapons would remain in the hands of the French president.
The French nuclear deterrent is air- and sea-based, with Rafale fighter jets and nuclear submarines being able to strike at any time, on the instruction of the French president alone.
In the early days of the Cold War, former president Charles de Gaulle developed a nuclear deterrent that was designed to be fully independent from the two dominant powers of the time, the Soviet Union and the US.
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In his televised address on the eve of a crucial European Union summit on defence, Mr Macron said France would spend more on defence - though he did not say how much more. He said there would be no tax increases to finance that, but tough choices would have to be made.
He said he wanted to believe that the US "will remain at our side," while adding that Europe had to be ready if that was no longer the case.
Mr Macron's address comes amid a flurry of European diplomacy to shore up support for Ukraine and try and mend ties between the US and Ukraine after an acrimonious meeting between Mr Trump and President Volodymyr Zelensky in the Oval Office last week.
France and the UK are aiming to finalise with Ukraine, possibly "in days", a peace plan to present to the US, while building bridges between the US and Ukraine before possible talks in Washington, diplomats have said.
Mr Macron's push to beef up French defence spending won't be easy as his government struggles to tame an unruly budget deficit.
