The build-up of Russian troops on the border with Ukraine has raised fears of a conflict over Moscow's pro-EU neighbour but it remains unclear what the Kremlin's intentions are.
"If there is an attack, there will be retaliation and the price (for Russia) will be very high," Macron said alongside German Chancellor Olaf Scholz on a visit to Berlin.
"We call for a deescalation of tensions and I want to also say how united Germany and France are on this subject," he added, following speculation that Berlin could be promoting a softer line regarding Russia.
"We are preparing in parallel a joint reaction and the response in case of aggression," he said, adding that Western powers were "totally united".
Scholz added: "We expect from Russia clear steps that contribute to a deescalation of the situation. We are all in agreement that a military aggression will trigger heavy consequences."
He also stressed that Moscow would have a "very high price" to pay if it violated Ukraine's territorial integrity.
But Macron also insisted that a "demanding dialogue" needed to continue with Russia and revealed that he would hold telephone talks with Putin on Friday.
These talks would provide the chance for Putin to give "clarification" over what Russia is planning in Ukraine, Macron said.
Several analysts predict Russia is considering some kind of intervention in Ukraine, although Moscow has insisted it is not planning a new attack on its neighbour following the annexation of Crimea in 2014.
Senior representatives of Germany, Russia, and Ukraine are also due in Paris in Wednesday to discuss Ukraine along with French officials in the so-called four-way "Normandy" format.
Macron accused Russia of behaving as a "power of disequilibrium" through its behaviour not just in Ukraine but also Belarus, the Caucasus and Moldova.
He said that the situation was worrying, and required Europe to stay united and to prepare a "joint response".
But he added: "It also means we should have a dialogue of clarification with Russia because I think that this dialogue is necessary to try to remove the ambiguities."
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