In an address to the nation, Macron said that the French were "legitimately worried" about the start of a "new era" after Trump began his second stint in the White House by reversing US policy on Ukraine and risking a historic rupture with Europe.

"I want to believe that the United States will stay by our side but we have to be prepared for that not to be the case," he said bluntly.

"The future of Europe does not have to be decided in Washington or Moscow," he added.

Trump has made clear his desire to swiftly end the war caused by Russia's 2022 full-scale invasion of Ukraine through direct negotiations with Moscow.

But Macron offered a stark picture of Russia's aggressive behaviour, which he said does "not seem to know borders" after its invasion of Ukraine.

"Russia has become, at the moment I am speaking to you and for the years to come, a threat to France and Europe," he said. "It would be madness to remain a spectator in this world of danger."

"Who can believe that this Russia of today will stop at Ukraine?" he asked. "Russia has become a threat for France and Europe."

But he warned Trump that "peace cannot be agreed at any cost" and there cannot be a ceasefire that is "too fragile".

- 'Won't fight today' -

Ahead of an EU summit Thursday on rearming the continent, he stressed the need for "new budget choices and extra investments" to boost defence spending in France.

Meanwhile, 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.

"I have decided to open up the strategic debate on the protection of our allies on the European continent through our nuclear deterrent," he said, while adding that any decision on nuclear weapons use would remain with the French head of state.

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.

Warning that "Russia can no longer be trusted to keep its word", Macron also said once a deal is signed Ukraine's allies must make sure it is "not invaded again by Russia".

He reaffirmed that European military forces could be sent to Ukraine if a peace accord was signed to guarantee "respect" of a peace deal.

A peace agreement for Ukraine would be backed "perhaps, by the deployment of European forces," Macron said.

"They won't go to fight today, they won't go to fight on the front line, but they would be there once a peace deal is signed, to guarantee it is fully respected," he said.

He added European military chiefs of staff would meet in Paris next week to discuss how to support Ukraine after a peace deal.

- Incomprehensible' -

Both Macron and British Prime Minister Keir Starmer held separate talks with Trump in Washington last week, followed by Ukrainian President Volodymyr Zelensky who was subjected to an excruciating public dressing-down by Trump and his Vice President JD Vance.

But Zelensky appears to be seeking to lower the temperature after Friday's White House bust-up with Trump where the US president accused the Ukrainian leader of not wanting peace and "gambling with World War III".

Zelensky Tuesday called for a "truce" in the sea and sky as a first step to ending the three-year war with Russia, echoing an idea evoked by Macron at talks in London hosted by Starmer at the weekend.

Meanwhile, Macron is mulling a joint visit to Washington alongside Zelensky and Starmer, the French government spokeswoman Sophie Primas said Wednesday.

The French presidency then sought to dampen expectations saying no new visit by Macron to Washington was being considered "at this stage".

Coincidentally, Macron after his address met Hungarian Prime Minister Viktor Orban at the Elysee. Orban is an admirer not just of Trump but also Putin, and has repeatedly broken a united EU front on Ukraine.

In another indication of tension with Washington, Macron on Wednesday called planned US tariffs on European products "incomprehensible", adding that he hoped to "dissuade" Trump from imposing them.