Iran and the U.S. have see-sawed between enmity and grudging diplomacy in the years since, with relations peaking when Tehran made the 2015 nuclear deal with world powers. But Trump unilaterally withdrew America from the accord in 2018, sparking tensions in the Mideast that persist today.

While rising U.S.-Iran tensions over Tehran's uranium enrichment jeopardize nuclear talks, three Iranian sources said on Tuesday that the clerical leadership lacks a clear fallback plan if efforts to resolve a decades-long dispute collapse.

DUBAI (Reuters) -Iranian and U.S. negotiators will resume talks on Friday in Rome to resolve a decades-long dispute over Tehran's nuclear ambitions, despite Iran's supreme leader warning that clinching a new deal might be insurmountable amid clashing red lines.