French President Emmanuel Macron said a decision by the United States to impose tariffs on European metals exports is illegal and a mistake which could close the door on discussions about other issues.
The French leader said he would talk to President Donald Trump on the subject later on Thursday.
"This decision is not only unlawful but it is a mistake in many respects," Macron said, adding that the US was responding to global imbalances with economic and commercial nationalism.
"Economic nationalism leads to war," Macron said.