A top European official branded President Donald Trump selfish and capricious Wednesday as E.U. leaders came together seeking ways to resurrect the flawed Iran nuclear deal.

E.U. Council President Donald Tusk delivered the rhetorical assault on the leader of Europe’s biggest ally as he observed that, given Mr. Trump’s recent diplomatic moves, “someone could even think ‘with friends like that, who needs enemies?’”

Mr. Tusk’s remarks preceded the Western Balkan summit in Sofia, Bulgaria, and were delivered to reporters before he chaired a meeting of the 28 leaders whose countries make up the bloc.

Listing Europe’s traditional challenges, ranging from the expanding power of China to the belligerence of Russia, Tusk said: “We are witnessing today a new phenomenon, the capricious assertiveness of the American administration.”

“Frankly speaking, Europe should be grateful to President Trump because thanks to him we have got rid of all illusions. He has made us realize that if you need a helping hand, you will find one at the end of your arm,” Tusk said.

Mr. Tusk then shared his views with the world via Twitter:

Looking at latest decisions of @realDonaldTrump someone could even think: with friends like that who needs enemies. But frankly, EU should be grateful. Thanks to him we got rid of all illusions. We realise that if you need a helping hand, you will find one at the end of your arm. — Donald Tusk (@eucopresident) May 16, 2018

E.U. leaders at the meeting were briefed on possible incentives to keep Tehran in the nuclear agreement despite a key player like the U.S. pulling out. Mr. Trump’s decision to end the deal struck by Barack Obama means that U.S. sanctions, held in check by a presidential veto until now, could impact European companies doing business with the Islamic theocracy.

“It is absurd to even think that the E.U. could be a threat to the U.S. We need to bring back reality in this discussion,” Tusk said.

Mr. Trump’s decision to relocate the U.S. embassy to Israel’s capital Jerusalem is also expected to be raised.

Belgian Prime Minister Charles Michel is calling for an international investigation into America’s decision to place its diplomatic mission in Jerusalem.

“It’s a moment that sends a shiver down your spine. Because there is a striking contrast between, on the one hand, an inauguration in great splendor, with smiles, and on the other hand, the drama, and families today that are in mourning with innocent children who are the victims of this situation,” Michel told state broadcaster RTBF.

“We knew that there was a great risk, that this decision to move moving the embassy would bring less security, bring tragedies, and sadly we were right,” he said.