But Mr. Zarif also was bitter about what he viewed as American double standards around the world, an assumption in Washington, he believed, that the United States only interfered in global affairs for good, not national interest, and that Iran did so out of perfidy.

At one point in 2014, he described to a reporter evidence that the United States had been shipping in damaged parts to an Iranian reactor, which he said could have led to an accident and loss of life. There was no evidence of his specific charge, but the United States has conducted similar operations against Iranian rockets and missiles and, famously, sabotaged an Iranian nuclear enrichment plant in the city of Natanz with a cyberweapon, part of a vast American covert operation code-named Olympic Games.

Mr. Zarif appeared to be at the center of the Iranian strategy to adhere to the nuclear deal he had negotiated, even after President Trump had abandoned it.

And as time went on, and American sanctions were reimposed, he appeared to have a dwindling constituency in Tehran and none in Washington.

Iranians are angry over never having received the promised economic rewards for their concession in the agreement to ship out 97 percent of their nuclear fuel and restrict the production of new fuel for 15 years. Mr. Zarif’s many meetings with Europeans in recent months to develop a barter system, going around reimposed American sanctions, amounted to little.

“Many around the world, particularly on this continent, speak eloquently about multilateralism, but they also need to walk the walk,” Mr. Zarif said in his last public address to the West, at the Munich Security Conference. The arrangement with Europe, he said, fell short of Europe’s effort to save the nuclear deal, and “Europe needs to be willing to get wet if it wants to swim against a dangerous tide of U.S. unilateralism.”

The Trump administration refused to communicate with Mr. Zarif. Senior officials declared he was powerless and asked reporters why they quoted him. He was in the same room once with Rex W. Tillerson, Mr. Trump’s first secretary of state, but the two never exchanged more than polite greetings. Mike Pompeo, Mr. Tillerson’s successor, never dealt with Mr. Zarif, American officials say.