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.

Iran's top diplomat warned Thursday that his country would take “special measures in defense of our nuclear facilities” if Israel continues to threaten Tehran's atomic sites, raising the stakes further ahead of a new round of talks with the United States.

The dispute over uranium enrichment is the flashpoint in U.S.-Iran talks, with Tehran refusing to scale back and Washington warning of weaponization.