Iran is on the agenda at a meeting of European Union foreign ministers in Brussels on Monday, after Trump set a 120-day deadline for US lawmakers and European allies to fix "disastrous flaws" in the deal or face a US exit.

The EU, which has staunchly defended the deal as the best way to thwart Iran's nuclear ambitions, is working on a response with France, Britain and Germany -- the three European signatories.

French Foreign Minister Jean-Yves Le Drian said as he arrived for the meeting that EU ministers would stay "firm" on the need to preserve the agreement, which he called "an essential element" of global efforts against nuclear proliferation.

"We have observed with interest that President Trump did not break the agreement, even if on the other hand he has made demands that sometimes look like ultimatums," Le Drian said.

Le Drian will visit Iran on March 5 to discuss Iran's ballistic missile programme and interference in conflicts around the Middle East -- both key complaints of Washington.