French president Emmanuel Macron has told US president Donald Trump that tariffs on steel and aluminium imports from the European Union are "illegal" and that the EU would respond in a "firm and proportionate manner", reports RFI.
Macron made his views clear to Trump by phone on Thursday after the US announced the tariffs on products from the EU, Canada and Mexico to come into effect as of Friday.
Europe is the single-largest source of US steel imports.
Macron warned that the decision would penalise everyone, including the US.
"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," he said.
"And nationalism is war. That's exactly what happened in the 30s."
EU chief Jean-Claude Juncker says the bloc is poised to announce counter-measures immediately.
France and other European nations will not negotiate while the sanctions were in effect, French finance minister Bruno Le Maire said en route to the G7 meetings in Canada on Thursday.