Mr. Trump’s Iran decision is part of a broader pattern of actions that have deeply frustrated America’s European allies. He also has threatened new tariffs in trade negotiations, quit the Paris climate accord and, in their view, expressed disdain for multilateral diplomacy.
Their anti-Trump mood was reflected in a speech on Wednesday by Donald Tusk, president of the European Council, who denounced what he called the “capricious assertiveness of the American administration.”
Mr. Juncker amplified the criticism on Thursday.
“We will not negotiate with the sword of Damocles hanging over our heads,” Mr. Juncker said. “It’s a matter of dignity, and it’s a matter of principle.”
Prime Minister Charles Michel of Belgium said Europeans were united in preventing the United States from determining the European Union’s economic interests.
Dalia Grybauskaite, the president of Lithuania, noted that Europe does not want a trade war with the United States over the Iran deal. “We are looking for technical solutions to protect our companies,” Ms. Grybauskaite said.
Despite their defiant response to Mr. Trump, it is unclear how effective any European Union measures would be in countering the restored American sanctions on Iran. Even as the summit meeting was underway, more big European-based companies signaled they would have to quit doing business with Iran to avoid running afoul of the American sanctions.
The world’s leading container shipping company, A.P. Moller-Maersk, said it would no longer do business in Iran, Reuters reported, while the Italian steel maker Danieli began scaling back on Iranian orders. On Wednesday, the French oil giant Total said it would have to divest from Iran unless it received an exemption from the American sanctions.