Mr. Trump and Secretary of State Mike Pompeo have both floated the possibility of a meeting at the United Nations. A similar effort for Mr. Trump and Mr. Rouhani to meet at the United Nations in 2017 collapsed.

The American sanctions against Iran were imposed last year, after Mr. Trump withdrew the United States from an accord that was struck with world powers in 2015 to limit Tehran’s nuclear program. The economic penalties have largely stopped foreign governments and businesses seeking to invest in Iran, or to buy its oil and other goods.

It is part of the “maximum pressure” campaign to isolate Iran and force it back into negotiations for a new deal — one that Mr. Trump wants to not only limit Iran’s nuclear program, but also stop its production of ballistic missiles and halt support for extremist groups across the Middle East, including Hezbollah, Hamas and, in Yemen, the Houthi rebels.



Though the sanctions campaign has crippled Iran’s economy, it has not stopped China from importing its oil.

And it has frustrated France and other close American allies, who are now working to create a barter system with Tehran that would keep financial channels open but not violate the American sanctions. Mr. Macron has also dangled the possibility of a $15 billion bailout to Iran to bring it back into compliance with the 2015 deal.

As he faces re-election next year, Mr. Trump has been searching for a diplomatic victory involving a host of adversaries, including North Korea, Venezuela and the Taliban in Afghanistan.

Signs of Mr. Trump’s softening against Iran have surfaced over the summer.

In June, and at the last minute, Mr. Trump called off missile strikes against Iran that his advisers had endorsed to punish Tehran for downing an unmanned American surveillance drone.

