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 are set to resume nuclear talks in Rome amid rising tensions, hard-line demands, and Israeli threats of military action. With uranium enrichment at the core of the standoff,

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.

Iran has multiple major sites associated with its rapidly advancing nuclear program, now the subject of several rounds of negotiations with the United States

Iran’s top diplomat is insisting that Tehran will never stop enriching uranium, further underlining the Islamic Republic’s red line in negotiations with the United States over its rapidly advancing nuclear program.

Iran's Supreme Leader Ayatollah Ali Khamenei slamm ed U.S. demands that Tehran end its uranium enrichment program, stating that he does not believe ongoing nuclear negotiations with the U.S. will yield results. Iran says its nuclear program is for civilian purposes and that its enrichment program is a source of national pride and not negotiable.

In the latest round of negotiations between the Trump administration and Iran, the US is pushing for zero nuclear enrichment on Iranian soil. But a Senior Iranian official tells CNN’s Fred Pleitgen Iran is “disappointed” with nuclear talks.