French President Emmanuel Macron on Thursday said he "deplored" the US move to impose harsh tariffs on steel and aluminium imports from the European Union, declaring it an "illegal" decision.
Warning about "nationalism", Macron told journalists he would talk later on Thursday with US President Donald Trump.
"I deplore the American decision" and "we will have a European position to take" based on international law, Macron said at the Elysee Palace.
"This decision is not in line with international trade law, so it is illegal," he said.
"I think this decision is a mistake in many ways because it responds to existing international imbalances in the worst way -- by breaking up and creating economic nationalism.
"And nationalism is war. That's exactly what happened in the 30s," he added.
Also in Paris, the secretary-general of the Organisation for Economic Co-operation and Development (OECD), Angel Gurria, reacted to the US decision to impose tariffs by calling to maintain multilateralism.
"We are at a critical moment not only for the future of multilateralism, but for the planet itself," he said in a speech.
"We need to save multilateralism because it's the only way forward as we increasingly confront challenges that are global in nature and therefore we don't know about borders."