Reuters - The deal struck in 2015 with three European countries, Russia, China and the United States gave Iran relief from a range of sanctions, allowing it to strike major business deals with Europe for the first time in years.
After taking one of the hardest lines in the negotiations, France has been quick to restore trade ties. Planemaker Airbus, oil major Total and automobile manufacturers Peugeot and Renault have all signed deals.
Some 50 French firms will take part in a Franco-Iranian economic forum on Tuesday at which more will be signed.
"Jean-Marc Ayrault is going to underline the importance that all sides which backed the deal strictly respect their commitments," Foreign Ministry spokesman Romain Nadal told a daily briefing.
Trump has called the deal, which imposes limits on Iran's nuclear activities, "the worst deal ever negotiated" threatening to annul it or seek a better agreement.
Despite their often fraught ties, the EU says it is in full agreement with China and Russia over the need to keep the nuclear deal alive.
"That the Iranians have been destabilized by Trump's election and statements is certain and I think they must be worried," a French diplomatic source said.
"But developing commercial ties strengthens the moderates in Iran. We want to reinforce them to show the population that the deal is good for them because the radicals won't be able to say that they have got nothing from it."
Despite the sanction relief, including on banking restrictions, Iran continues to struggle to access Western finance, partly due to banks’ fears about penalties related to remaining U.S. sanctions.
France's relationship with Shi'ite Muslim Iran is complicated by its political and commercial ties with Sunni Gulf Arab states, especially Saudi Arabia, Tehran's main regional rival.
Ayrault was in Riyadh on Jan. 24 partly to discuss the trip to Tehran with an eye on Iran's role in the region, especially in Syria where Paris and Riyadh back opponents to Iranian ally President Bashar al-Assad.
"We don't agree on Syria and will remind them that France and the European Union are directly concerned by the Syria crisis and among the first to suffer its consequences. So we must have a role in helping find a solution," the source said.