French president has warned US president that tariffs on steel and aluminium imports from the European Union were illegal.

French president Emmanuel Macron also told US president Donald Trump late Thursday that the EU would respond in a firm and proportionate manner, according to the Elysee Palace.

The phone call between the French president and his US counterpart came after the US announced steep metals tariffs would be imposed on the European Union, Canada and Mexico as of midnight on Thursday.

French president, who has forged a good relationship with his American counterpart, spoke to Trump on the phone, urging him to take part in negotiations with the EU, China and Japan to strengthen the rules of the World Trade Organisation.

Macron called the decision to impose tariffs a "mistake", warning that "economic nationalism" would penalise everyone including the US.

Earlier Thursday Macron told journalists at the Elysee Palace that he deplored the American decision.

"Nationalism is war. That's exactly what happened in the 30s," French president added.

Meanwhile, French Finance Minister Bruno Le Maire said Thursday that France will refuse to enter into trade talks with the United States while punishing steel and aluminum tariffs are in effect.