ROME (AP) — Iran and the United States prepared for a fifth round of negotiations over Tehran’s rapidly advancing nuclear program Friday in Rome, with enrichment emerging as the key issue.

Iran and the United States concluded a fifth round of high-stakes nuclear talks in Rome on Friday amid growing skepticism in Tehran about the chances of a deal as Washington hardens its position.

The U.S. and Iran ended talks with "some but not conclusive progress" on nuclear negotiations, according to an Omani mediator. But the countries still appear far apart, with the U.S. saying Iran cannot be allowed to enrich uranium for civilian use.