On Wednesday European Council president Donald Tusk had laid into the US President.

"With friends like these, who need enemies," he'd said, referring to Donald Trump's trade tariffs and his abandoning of the Iran nuclear deal.

Then on Thursday came President's Trump's riposte:

"Frankly the EU, outside of China and a couple of others, treats us on trade as badly as you can be treated."

At the moment the EU has secured temporary exemptions from a 25 percent steel tariff and a 10 percent aluminum tariff, both introduced by President Trump and primarily targetting China,

"The European Union has been terrible to the United States on trade, terrible to our workers. Last year, we had a trade deficit of 151 billion dollars. And I know Jean-Claude very well, and I know Donald very well and I like them both, but they're very tough and we never had anybody negotiating for us," he said.

Trading blows with other world leaders has not been uncommon during Trump's presidency.

Also on Thursday President Trump again attacked Germany for not paying as much as it should into NATO's budget.

The alliance says its members should pay them two percent of their GDP, but Germany only pays 1.3 percent.