U.S. president Donald Trump greets supporters during a campaign rally at Scheels Arena on June 27, 2018 in Fargo, North Dakota | Justin Sullivan/Getty Images Trump: EU was ‘set up to take advantage’ of US ‘We can’t let that happen,’ US president said.

Donald Trump has accused the EU of going after the United States' "piggybank," amid an ongoing trade dispute over tariffs.

"We love the countries of the European Union. But the European Union, of course, was set up to take advantage of the United States," Trump said at a rally in North Dakota on Wednesday. "And you know what, we can't let that happen."

His latest comment comes amid a continued escalation in the trade war between the U.S. and the rest of the world, which began when Trump slapped a series of tariffs on some countries at the end of March, before extending them to close allies such as the EU at the end of May. Brussels responded with retaliatory duties, which came into force last week, prompting iconic American motorcycle maker Harley-Davidson to announce it would move some of its production abroad.

Trump on Wednesday doubled down on his claims the EU is cheating the U.S on trade, saying the U.S. last year lost $15 billion on trade with the EU.

"Because they send the Mercedes in, they send the BMWs in, they send their products in [and when] we sent things to them, they say 'No, thank you, we don't take your product," Trump said. "For all you free traders out there, that's not free trade, that's stupid trade."

Trump — who on Tuesday extended an invitation to European Commission President Jean-Claude Juncker to discuss trade — has insisted the EU will ultimately back down, but Brussels says it won't give in to bullying.

“There are no [trade] talks planned,” EU trade chief Cecilia Malmström said Tuesday, adding that "there had to be consequences [when] you do not respect international global rules."

France's economy minister, Bruno Le Maire, has also insisted Europe won't back down. “If the United States hits us again with a 20 percent increase on cars, we will respond again. We don’t want an escalation, but we are the ones being attacked,” he said.