Germany acknowledged it could be hard to protect companies doing business with Iran as a senior USA official renewed a threat of sanctions against European firms following Washington's decision to pull out of a nuclear deal with Tehran.
Mr Trump's announcement last week that he was withdrawing the USA from the landmark Iran deal inflamed regional tensions and threw European investments from oil to aerospace into jeopardy.
Trump's action has been met with dismay among America's allies in Europe and Asia and with scathing criticism and opprobrium in the U.S. political circles and the liberal press.
"If Mr. Trump thinks he is sending a strong message of resolve to North Korea, he is again mistaken".
But on Sunday US Secretary of State Mike Pompeo said Washington was keen to hammer out a new agreement with its European partners to counter Tehran's "malign behaviour".
German leader Angela Merkel also told Trump on a visit to Washington late last month that the nuclear deal was insufficient in itself to curb Iran's ambitions in the region.
It also demanded that Iran cease supplying weapons to the Houthi rebels, who have been at war with Tehran's archenemy Saudi Arabia, end cyberattacks against the USA and its allies, stop menacing US military ships in the Persian Gulf and abandon its rhetoric about destroying Israel.
Following the choice of the White House, which received the applause of Israel and several Arab nations, the Islamic Republic declared that it was ready to resume the enrichment of uranium "on a large scale" and "without any restriction".
However, he added, "We are not going to get into confrontation", with the U.S.
Meanwhile, the Kremlin said that Russian Federation and its ex-Soviet allies will sign a free trade pact with Iran. All 15 UNSC members have endorsed the Iran deal, enshrining it through a resolution as part of global law.
The grouping includes Kazakhstan, Belarus, Armenia, and Kyrgyzstan.
However on Tuesday the USA hit Iran's central bank governor with sanctions.
The meeting is being hosted by the European Union's foreign policy chief Federica Mogherini.
"This deal is not a bilateral treaty". If "everybody simply does what they want, then that's bad news for the world", she said.
Europe's options, however, are limited.
Iran is seeking assurances that European, Russian and Chinese companies will continue to do business with Iran, even in the face of threats that such companies might have to face USA sanctions.
"Instead", she wrote, "it is the (US) that is about to violate the very agreement it negotiated by reimposing nuclear-related sanctions while Iran remains in compliance".
Planemakers Airbus and Boeing, oil companies and auto manufacturers like France's Renault and Peugeot could be among companies hardest hit.
Britain, France, and Germany - along with Russian Federation and China - all have said they remain committed to honoring the deal and believe it remains the best way to ensure Iran does not resume development of nuclear weapons.
Facing that reality, Le Maire said the European Union should strengthen its own legal arsenal against any such future USA threats.
"It's possible", he said.
But the reach of the U.S. financial system, the dominance of the USA dollar, Trump's efforts to weaken the WTO and the presence of European companies' operations in the United States all weaken any potential EU measures.
Le Maire also proposed creating a European body that would have the same kind of powers that the U.S. Justice Department has to punish foreign companies for their trade practices.