"Sanctions have been lifted but really things are still not very clear," a source at a major French bank told AFP on condition of anonymity.
US and French interpretations on the current state of play are "not aligned", the source said. "We shall not be taking any new initiative in this domain."
The sealing of a nuclear deal with world powers has ushered Iran in from the diplomatic deep freeze, opening the door to a raft of lucrative new partnerships.
France has already hailed a new era after welcoming Iranian President Hassan Rouhani, who sealed a host of post-sanctions deals last week on a visit to Paris, the headliner the purchase of 118 Airbus aircraft.
But when it comes to what oils the wheels, high finance, there is hesitation, at least on the part of European banks.
"The hefty fines levied on these financial institutions during the sanctions has made them particularly wary," Farhad Alavi, a lawyer specialising in trade issues including sanctions, told AFP from Washington.
"European banks are not only confronted with potential sanctions risks, but also other exposure points under international banking regulations and practices," Alavi added.
Prudence is the watchword for bankers who have had their fingers burned before in the shape of swingeing fines handed down by US regulators.
The Elysee Palace says France has agreed deals worth upwards of $15 billion with the Islamic Republic. Yet the nitty gritty of how the investments will be drawn up and financed requires hands-on banking.
In the past, some banks were too pro-active towards Tehran and saw Washington extract a heavy price for violating the old sanctions regime.
The most spectacular example, which is still on every banker's mind, was a record $8.9 billion fine imposed on BNP Paribas in 2014.
The issue is also taxing banking minds elsewhere in Europe, including Germany.
"Deutsche Bank has noted the easing of American and European sanctions against Iran," said a spokesman for the German giant which last November took a $258 million fine for doing business with US-sanctioned entities including Iran and Syria.
"Until further notice the group will stick to its decision and not undertake Iran-linked business," the Deutsche spokesman insisted.
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"There is uncertainty," says Yves-Thibaut de Silguy, vice-chairman of Medef International, which offers private sector liaison for the likes of the World Bank and other development banks and international organisations.
De Silguy told France Info radio last week that while Washington had lifted nuclear sanctions other US measures -- notably to stem terror funding -- remain in place.
French minister of state for foreign trade, Matthias Fekl, said Thursday he had requested "clarification" from Washington on sanctions lifting parameters and timetabling.
It will fall to the US Treasury Department offshoot the Office of Foreign Assets Control, which oversees sanctions enforcement, to provide that information.
Thierry Coville, of the French Research Centre for International and Strategic Studies (Iris), believes Washington is happy to let uncertainty persist.
"It could be a US policy to say, 'careful, it's complicated', so people don't understand what's going on and think they (the sanctions) remain in place," says Coville.
"Legally, the banks can do things" but still require "all the assurances in the world before they can return to Iran," Coville said.
He added that "what BNP Paribas did was not actually illegal" but Washington "still has the means to put pressure on the banks".
Even if some are ready to position themselves for a return to the Iranian market the banks are keeping quiet on their intentions.
"I don't see how large groups can seal contracts without financial support" being in place, says Coville.
Pascal de Lima, chief economist with Economic Cell group, believes Iran has strong potential yet remains a "high risk country" owing to "the geopolitical situation with Israel."
For the banks, he also highlights the "confidence undermined through the BNP Paribas sanction".
Seeking to reassure, Paris last Tuesday unveiled an accord offering state guarantees to back French investments in Iran through credit management firm Coface in order to cover onsite non-payment risks.
Fekl also stressed that France has set up teams of sanctions specialists working out of the treasury and the foreign ministry to address questions firms may have regarding the legitimacy of their Iranian operations and whether they conform to US legislation.
Even so, Coville laments a "strategic mistake which is today being paid for" to allow OFAC to place "direct pressure on the European banks" when it comes to a return to Iran.
"Politically, this is lamentable on the part of the Europeans. This is now a financial and geopolitical weapon that the United States won't shirk from using again in other circumstances."