President Emmanuel Macron said that Europe can no longer count on military support from the US were the continent to be attacked in future.
In an address to the French people, Mr Macron said he was willing to discuss offering European allies the protection of France's nuclear capabilities.
"I want to believe that the United States will stand by us. But we have to be ready if that is not the case.
"Given the Russian threat that I have just described, European states must be able to defend themselves better and deter any aggression ... We must equip ourselves better, raise our defence posture, and this for peace, even to deter.
“In this respect, we remain committed to NATO and our partnership with the United States of America. But we must do more. Strengthen our independence in defence and security matters."
EU leaders are set to address the issue of nuclear deterrence, among other issues, during a special summit in Brussels on Thursday, focusing on support for Ukraine and European defence.
France and Britain are Europe's only two nuclear powers.
Mr Macron also said he hoped to convince US President Donald Trump not to impose tariffs on imports from Europe.
Washington has threatened to impose 25% tariffs on European goods.
European countries are scrambling to boost defence spending and maintain support for Ukraine after Trump froze US military aid to Kyiv and fuelled doubts about Washington's commitment to its European NATO allies.
Mr Macron’s address comes amid a flurry of European diplomacy to shore up support for Ukraine and try and mend ties between Washington and Kyiv after an acrimonious meeting between Trump and President Volodymyr Zelensky in the Oval Office last week.
France and Britain are aiming to finalise with Ukraine, possibly "in days", a peace plan to present to the United States, diplomats have told Reuters.
