The EU chief negotiator for the Iran nuclear deal talks said Tuesday that "much more hard work" was needed to rescue the 2015 landmark agreement, following the latest discussions in Vienna.

EU diplomat Enrique Mora hailed "progress made over the last two weeks" but said "ongoing challenges" remained to put the accord — which curbs Iran's nuclear programme in exchange for sanctions relief — back on track.

But for Iranian President Hassan Rohani, the "negotiations have achieved 60-70 percent progress," according to IRNA news agency.

"If the Americans act honestly, we will reach a conclusion in little time," Rohani was quoted as saying.

The deal was thrown into question when the US withdrew in 2018 and sanctioned Iran, which in turn started ramping up its nuclear activities.

US President Joe Biden is seeking to revive the agreement.

Diplomats from Britain, China, France, Germany, Iran and Russia have been meeting regularly since early this month in a luxury Vienna hotel, while US diplomats are participating indirectly in the talks from a nearby hotel.

"Much more hard work needed," Mora wrote on Twitter after a fresh round of talks.

He added a third expert group had been created to address "sequencing issues" after two groups were set up to look into nuclear issues and sanctions lifting.

Iran insists it can reverse its nuclear activities — including producing uranium enriched to 60 percent purity, far above the deal's threshold — but only once sanctions imposed by former US president Donald Trump are removed.

Talks are set to continue next week, according to an EU statement, with participants noting a new sense of urgency.

Mikhail Ulyanov, Russia's ambassador to Vienna, wrote on Twitter that the parties "decided to take a break to allow the delegations to do homework and consult with the capitals".

Ulyanov on Monday had said negotiations had entered "the drafting stage" though "practical solutions" were "still far away".

Russia says Iran nuclear talks enter 'drafting stage'
Vienna (AFP) April 19, 2021 –

A Russian diplomat taking part in talks to save the landmark Iran nuclear deal said Monday that the negotiations had entered "the drafting stage" though solutions to some of the issues were "still far away".

The 2015 agreement to curb Iran's nuclear programme in exchange for sanctions relief has been left hanging by a thread since the US withdrew from the pact in 2018 and re-imposed sanctions, prompting Tehran to in turn step up its nuclear activities.

Diplomats from the parties to the deal — Iran, Britain, China, France, Germany and China — have been meeting in Vienna since early this month to find a way to get the pact back on track with US participation under the new Joe Biden administration.

"Summing up the results of two weeks of deliberations on JCPOA restoration we can note with satisfaction that the negotiations entered the drafting stage," Russian ambassador to Vienna Mikhail Ulyanov wrote on Twitter, referring to the acronym of the deal's formal name.

"Practical solutions are still far away, but we have moved from general words to agreeing on specific steps towards the goal," he added.

Separately, the International Atomic Energy Agency and Iran on Monday began "to engage in a focused process" aimed at clarifying IAEA queries about the possible previous presence of nuclear material at undeclared sites, the UN's nuclear watchdog said.

"As agreed in March… the discussions are being held at the level of technical experts. Today's meeting took place in Vienna," the IAEA said in a statement to AFP.

The EU, Russia and Iran all hailed progress at the talks Saturday following an attack on Iran's Natanz nuclear facility, which Tehran blamed on arch-foe Israel.

On Friday, Tehran also announced that it was producing uranium enriched to 60 percent purity, taking the country closer to the 90-percent level required for use in a nuclear weapon and far above the threshold allowed by the 2015 deal.

Iran has said it will reverse steps taken so far if the US lifts sanctions imposed under the administration of former president Donald Trump.

US National Security Advisor Jake Sullivan told Fox News on Sunday that the US wanted to be sure of Iran's compliance.

"The United States is not going to lift sanctions, unless we have clarity and confidence that Iran will fully return to compliance with its obligations under the deal that it will put a lid on its nuclear programme," he said.

Iran's foreign ministry spokesman Saeed Khatibzadeh said during a weekly press conference on Monday that the negotiations were "not at the end of the road".

"We are at the beginning of the road of these difficult talks," he said.

Iran delegation head Abbas Araghchi had said Saturday that "a new agreement is taking shape" but warned that it won't be easy.