As the bloc paved the way for retaliation, its 28 leaders meeting in the Bulgarian capital Sofia made a rare demonstration of unity in the face of what EU President Donald Tusk called the "capricious assertiveness" of the Trump administration.
In a letter to European Union leaders ahead of their meeting Wednesday night in Sofia, Donald Tusk said that with friends like Donald Trump, the European Union could ask who needs enemies. The EU and U.S. are friends and partners, therefore United States tariffs can not be justified on the basis of national security'.
According to the source, they reaffirmed that they will "not negotiate with a gun at its head", but they said they are ready to talk with the United States once its decides on a permanent tariffs exemption for the EU.
U.S. President Donald Trump has imposed import duties of 25 percent on steel and 10 percent on aluminum on grounds of national security, but granted European Union producers a temporary exemption until June 1 pending the outcome of talks.
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. This is the only real alternative.More news: Theresa May confirms exit form customs union after Brexit
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The EU leaders were also due to discuss the deaths of dozens of Palestinians in Gaza after Trump moved the U.S. embassy to Jerusalem, in another move that the Europeans had strongly opposed, but there were no details on that discussion.
However, the former Polish Prime minister also insisted that "Europe must do everything in its power to protect, in spite of today's mood, the transatlantic bond".
In his criticism of the accord, which the other signatories Russian Federation and China also want to uphold, Trump has said it did not go far enough in restraining Iran's ability to develop nuclear weapons, while not addressing its missile programme and involvement in various conflicts in the Middle East.
Last week, German chancellor Angela Merkel said that "it is no longer the case that the United States will simply just protect us".
The EU has called for "utmost restraint" after Israeli forces killed 60 Palestinians during clashes and protests along the Gaza border against the opening of the USA embassy in Jerusalem, the conflict's bloodiest day in years.
"They think they can make the Iranian nation surrender by putting pressure on Iran, through sanctions and even threats of war".