European Council President Donald Tusk lashed out at the United States president, blasting his decision to pull out from the Iranian nuclear deal and stirring up trade disputes with other countries, and lamenting that one does not need enemies with friends like Trump.
Mr Trump's decision to walk away from the landmark nuclear deal with Iran - to which the UK, France, Germany, Russia and China are co-signatories - is being linked by the European Union with the USA administration's refusal to exempt the bloc from steel and aluminium tariffs.
He also added that "looking at the last trump, someone could even think that such friends do not need enemies".
These include protecting European companies dealing with Iran from US sanctions, which in practice would be very hard, allowing the European Investment Bank to invest there and coordinating euro-denominated credit lines from EU states.
The EU's hopes have been complicated by the fact that European companies would also be exposed to USA sanctions imposed on anyone doing business in Iran.
Tusk demanded a permanent exemption from the threatened tariffs for the European Union, and said any claim by the USA that such tariffs are justified for national security would be "absurd".
European leaders will seek to agree a common stance on Wednesday towards threatened USA import tariffs on steel and aluminium, balancing the views of those most fearful of a trade war and those determined not to be bullied into concessions.
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"We would stay calm here, there is no need for the meeting on Wednesday to take decisions on specific modalities of the mechanisms that are to shield the interests of European companies", the official said.
Tusk told a news conference in Sofia, Bulgaria, on Wednesday that "Europe should be grateful" to Trump since he has "rid Europe of all illusions" with the trade dispute and withdrawal from the Iran nuclear agreement, officially known as the Joint Comprehensive Plan of Action (JCPOA).
Earlier on Wednesday, EU foreign policy chief Federica Mogherini briefed top officials at the European Commission on talks she had held the previous evening with Iranian Foreign Minister Mohammad Javad Zarif and his German, French and British counterparts.
"I have no doubt that in the new global game, Europe will either be one of the major players, or a pawn". "This means a permanent exemption from USA tariffs on aluminium and steel if we are to discuss possible trade liberalisation with the U.S".
Europe can try to persuade companies to keep dealing with Iran, but just the threat of USA sanctions already has companies nervous.
Behind their message of unity and firmness, some member states seem open to tolerating limited quotas from the United States on metals imports while others want a harder line, diplomats said.
But the reach of the USA financial system, the dominance of the dollar and the presence of European companies' operations in the United States all weaken any potential EU measures.