Iran’s foreign minister, Mohammad Javad Zarif, said on Saturday that Tehran was closing in on an agreement to sell oil to European nations despite American threats of sanctions against any countries that do business with Iran.

If the arrangement comes to fruition — some British and French officials say they have their doubts — it would constitute the most open break between President Trump and European allies that objected vociferously to his decision to pull out of the 2015 nuclear deal.

Several of those nations openly confronted Mr. Trump on Wednesday, when he led a United Nations Security Council meeting about weapons of mass destruction. They argued that he was throwing away the best chance the world has to keep Iran from building nuclear weapons in coming years.

In an hourlong conversation with reporters, Mr. Zarif, who negotiated the nuclear accord with John Kerry, who was then the secretary of state, sounded far more optimistic than he had in recent months that he could peel away America’s traditional allies to break Mr. Trump’s effort to cut off Iran’s revenues.