Iranian and US negotiators closed on Friday a fifth round of nuclear talks in Rome with "some but not conclusive progress," mediator Oman said, after a public disagreement over Tehran's uranium enrichment.

The talks, which began in April, are the highest-level contact between the foes since the United States quit a landmark 2015 nuclear accord during President Donald Trump's first term.

Since returning to office, Trump has revived his "maximum pressure" campaign on Iran, backing talks but warning of military action if diplomacy fails.

Iran wants a new deal that would ease the sanctions which have battered its economy.

"The fifth round of Iran-US talks has concluded today in Rome with some but not conclusive progress," Omani Foreign Minister Badr Albusaidi said on X, adding that he hoped "the remaining issues" would be clarified in the coming days.

Iranian foreign ministry spokesman Esmaeil Baqaei had earlier said that chief US negotiator Steve Witkoff had left the talks "due to his flight schedule."

The fourth round of talks, in the Omani capital Muscat, ended with a public spat over enrichment.

Witkoff said Washington "could not authorise even one percent" enrichment – a position Tehran called a red line, citing its rights under the nuclear Non-Proliferation Treaty. (AFP)