"In some places trade has been to blame for the pains of globalisation or they used it as a scapegoat or they think we can live behind walls and borders," European Trade Commissioner Cecilia Malmstroem said at a conference in Brussels.
"Recently we have seen how it is used as a weapon to threaten and intimidate us. But we are not afraid, we will stand up to the bullies," Malmstroem said.
The tycoon's threat is part of a dispute over an announcement of tariffs on steel and aluminium imports, although the Trump administration has said it will consider exceptions and has already spared Mexico and Canada.
The announcement of duties of 25 per cent on imported steel and 10 per cent on aluminium has stung the EU and other major partners, coming as a surprise to allied countries and to many in Washington.
Malmstroem fired back at Trump after holding fruitless talks in Brussels on Saturday with US Trade Representative Robert Lighthizer aimed at defusing the row and avoiding an all-out trade war.
Those efforts are expected to continue this week, though no details for further negotiations have yet been announced.
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