PARIS — Before the ink was even dry on the Iran nuclear deal, European leaders and executives were heading to the airport to restart trade with an Iranian market described in almost feverish terms as “an El Dorado” and potential “bonanza.”

Germany sent a delegation five days after the signing of the accord in Vienna on July 14. The French foreign minister, Laurent Fabius, arrived in Tehran on Wednesday. Italian government ministers will get there on Tuesday. Business leaders are to follow soon. They will include 70 to 80 top executives of France’s largest companies in September.

Despite the hints of a gold rush, however, the probable opening of Iran’s market holds substantial risks for businesses, and makes it more complicated diplomatically to pull back anew if Iran again pursues the capacity to make a bomb.

Perhaps most important, the United States — virtually alone — is largely missing as an economic player. The nuclear agreement does little to lift a raft of American sanctions stemming from Washington’s listing of Iran as a state sponsor of terrorism and violator of human rights.