US President Donald Trump has "reignited" tensions with his EU counterparts as he called the Germans "bad, very bad" for their trade surplus with the US.

Trump vowed to block German car exports to the US during a meeting with top EU leaders in Brussels on Thursday, according to German news magazine Der Spiegel.

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"The Germans are bad, very bad," Trump said, according to participants in the room who spoke to the magazine.

"See the millions of cars they are selling in the US. Terrible. We will stop this," Trump said during the meeting with European Commission President Jean-Claude Juncker and European Council President Donald Tusk.

Both Juncker and Tusk showed solidarity with the Germans at the meeting and contradicted Trump's rebuke. 

Juncker, later, dismissed the claims on Friday, saying that the German media reports were exaggerated. "He did not say that the Germans were behaving badly," Juncker told reporters in Sicily ahead of G-7 talks.

"He was not aggressive at all and anyway we have taken the defence of the Germans," he said.

"I was making clear that the US cannot compare their trade situation with individual member states of the European Union. 

"They have to compare their performances with the global performances of the European Union, and I made it clear that the commission is charged with trade issues and not the member states," Juncker added.

Trump has long voiced his frustrations with Germany's trade surplus with the US, insisting that German imports have damaged the US manufacturing industry.

In January, he threatened to slap a 35 per cent tax on German auto imports.

White House Economic Adviser Gary Cohn on Friday defended the President's remarks.

"He said they're very bad on trade but he doesn't have a problem with Germany… He said 'I don't have a problem with Germany, I have a problem with German trade'," Cohn said.

The closed-door meeting was part of broader talks among world leaders over defence, trade and the environment.

He also attacked NATO members for failing to meet the military alliance's target to spend two per cent of GDP on defence.