Forty-two countries approved, at France's initiative, a declaration on the principles that must guide Europe's security.
This warning comes as Marine Le Pen, the frontrunner in the presidential election, intends, if elected, to end financial aid to Ukraine after a period of six months.
The National Rally candidate is thus calling aid to Kyiv into question. Ukraine has been invaded by Russia since 2022.
"My dear fellow citizens, what is at stake in Ukraine concerns us directly,"the head of state said.
Helping Ukraine defend itself means protecting France and the French people, according to him.
The first priority he sets is to help Ukraine get through the winter. That means maintaining financial support and helping the country protect its population, its power plants and its electricity grids.
The second priority is to work with Ukraine toward a just and lasting peace. Europe must play its full part, because the security of the continent also depends on that peace.
He said that at the European Council the day before, unity had been reaffirmed on this point.