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.

The fifth round of Iran–US nuclear talks in Rome ended without breakthrough as uranium enrichment remains a flashpoint. The US insists on zero enrichment, while Iran calls it non-negotiable. Tehran rejected American calls to broaden the agenda beyond nuclear issues to include missiles and regional militias.

Over the last month and a half, there have been ups and downs in the nuclear talks that often feels like a roller coaster ride.

Senior Iranian cleric Ahmad Khatami criticized President Trump amid rising tensions as nuclear talks continue in Rome.

President Trump discussed his plans for a nuclear deal with Iran Thursday — ahead of Friday talks in Rome between US and Iranian emissaries. Trump expressed his condolences to Israeli Prime Minister Benjamin Netanyahu about the murder of two Israeli diplomats in DC on Wednesday during the discussion.

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.