Iran and six governments said they held "substantive and detailed discussions" on all elements of a possible nuclear deal, the Wall Street Journal reports.
Still, "intensive work will be required to overcome [remaining] differences," Iranian Foreign Minister Mohammad Javad Zarif and European Union foreign policy chief Catherine Ashton added in shared remarks issued on Wednesday, as they ended a two-day multilateral atomic meeting.
Ashton, who represents the five permanent U.N. Security Council member nations and Germany, said the sides would meet again on May 13.
On Tuesday, Iranian Deputy Foreign Minister Abbas Araqchi said his country's negotiators had "narrowed" their differences with counterparts from China, France, Germany, Russia, the United Kingdom and the United States, Agence France-Presse reports. He did not elaborate on specific developments in the talks, aimed at striking a deal to eliminate international sanctions on Iran if the Persian Gulf power accepts long-term limits on its atomic activities.
Amid reports of possible progress in a dispute over Iran's unfinished heavy-water reactor, Araqchi stressed that his country would only consider certain moves to assuage fears that the site could generate bomb-usable plutonium, Reuters reported. Tehran insists the Arak reactor and its other atomic assets have strictly peaceful aims, but that contention faces skepticism in Washington and European capitals.
"Arak will remain [a] heavy-water reactor ... but there are technical ways to decrease concerns over its activities," he said.
The Iranian diplomat added that his country "will not stop or suspend its uranium enrichment work under any circumstances."
Meanwhile, U.S. Secretary of State John Kerry said Iran is now situated to produce enough fuel for a nuclear weapon in two months, AFP reported.