Any attempts at waging trade wars are a complete mistake, Polish Prime Minister Donald Tusk said Monday, after President Donald Trump said over the weekend that he would impose hefty new tariffs on goods from Mexico, Canada, and China.

"Poland will for sure be a country that encourages common sense and caution. But we also have to say clearly that any plans to introduce customs and (wage) trade wars are a complete mistake," he told journalists.

"I hope that such a firm, clear, friendly, but tough European position will get across to the American administration."

EU leaders are meeting Monday, bracing for the possibility that they too will face punishing U.S. trade levies.

"We must be unquestionably united. It is worth doing everything possible to ensure that in the face of a Russian threat or Chinese expansion, we do not fight between allies," Tusk told reporters before leaving for Brussels.