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

Iran and the United States will hold talks Friday in Rome, their fifth round of negotiations over Tehran’s rapidly advancing nuclear program.

Washington insists that Tehran can’t continue to enrich uranium under a deal, warning that Iran’s ability to do so opens the way for the country to ultimately attain a nuclear weapon, which President...