By Parisa Hafezi and John Irish

DUBAI (Reuters) -Iranian and U.S. delegations wrapped up a fifth round of talks in Rome on Friday and signs of some limited progress emerged in the negotiations aimed at resolving a decades-long dispute over Tehran's nuclear ambitions.

Despite both Washington and Tehran taking a tough stance in public ahead of the talks on Iran's uranium enrichment, Iranian Foreign Minister Abbas Araqchi said there was potential for progress after Oman made several proposals during the talks.

"We have just completed one of the most professional rounds of talks ... We firmly stated Iran's position ... The fact that we are now on a reasonable path, in my view, is itself a sign of progress," Araqchi told state TV.

"The proposals and solutions will be reviewed in respective capitals ... and the next round of talks will be scheduled accordingly."

A senior U.S. official said the talks lasted more than two hours and were both direct and indirect with Omani mediators.

"The talks continue to be constructive – we made further progress, but there is still work to be done. Both sides agreed to meet again in the near future. We are grateful to our Omani partners for their continued facilitation," the official said.

The stakes are high for both sides. President Donald Trump wants to curtail Tehran's potential to produce a nuclear weapon that could trigger a regional nuclear arms race and perhaps threaten Israel. The Islamic Republic, for its part, wants to be rid of devastating sanctions on its oil-based economy.

Omani Foreign Minister Badr Albusaidi said on X the talks between Araqchi and Trump's Middle East envoy Steve Witkoff had ended "with some but not conclusive progress".

Ahead of the talks, Araqchi wrote on X: "Zero nuclear weapons = we Do have a deal. Zero enrichment = we do NOT have a deal. Time to decide." 

Among remaining stumbling blocks are Tehran's refusal to ship abroad its entire stockpile of highly enriched uranium - possible raw material for nuclear bombs - or engage in discussions over its ballistic missile programme.

Diplomats have said reaching a concrete deal before the summer would technically be impossible given the complexities of an accord. In the meantime, a senior Iranian official involved in nuclear talks with the U.S. said "if Washington drops its 'zero enrichment' demand, a political agreement is feasible."

STUMBLING BLOCKS

U.S. Secretary of State Marco Rubio said on Tuesday that Washington was working to reach an accord that would allow Iran to have a civil nuclear energy programme but not enrich uranium, while acknowledging that this "will not be easy".

Iranian Supreme Leader Ayatollah Ali Khamenei, who has the last say on matters of state, rejected demands to stop refining uranium as "excessive and outrageous", warning that such talks were unlikely to yield results.   

Iran says it is ready to accept some limits on enrichment, but needs watertight guarantees that Washington would not renege on a future nuclear accord.

Trump in his first term in 2018 ditched a 2015 nuclear pact between major powers and Iran. Since returning to office this year, he has restored a "maximum pressure" campaign on Tehran and reimposed sweeping U.S. sanctions that continue to hobble the Iranian economy. 

Iran responded by escalating enrichment far beyond the 2015 pact's limits.

Wendy Sherman, a former U.S. undersecretary who led the U.S. negotiating team that reached the 2015 agreement, earlier said that Tehran presents enrichment as a matter of sovereignty.

"I don't think it is possible to get a deal with Iran where they literally dismantle their programme, give up their enrichment, even though that would be ideal," she told Reuters.

The cost of failure of the talks could be high. Iran's arch-foe Israel sees Iran's nuclear programme as an existential threat and says it would never allow the clerical establishment to obtain nuclear weapons. Tehran says it has no such ambitions and the purposes are purely civilian.

Israel's strategic affairs minister and the head of its foreign intelligence service, Mossad, were also due to be in Rome for talks with the U.S. negotiators, a source aware of the matter told Reuters.

Araqchi said on Thursday that Washington would bear legal responsibility if Israel attacked Iranian nuclear installations, following a CNN report that Israel might be preparing strikes.

(Reporting by Parisa Hafezi in Dubai and John Irish in Paris; additional reporting by Steve Holland; writing by Parisa Hafezi; editing by Alexandra Hudson, Mark Heinrich, Kevin Liffey and Andrew Heavens)