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.

Iran and the United States made “some but not conclusive progress” Friday in a fifth round of negotiations in Rome over Tehran’s rapidly advancing nuclear program, the talks’ Omani mediator said.

The sticking point to a framework agreement is whether Iran would be allowed to keep enriching uranium.