Ambitious nuclear talks between Iran and six world powers entered a second day in Vienna on Wednesday with Tehran's foreign minister saying a deal was "totally achievable".
Michael Mann, spokesman for the powers' lead negotiator and EU foreign policy chief Catherine Ashton, said on Twitter that day one's talks were "substantive" and "useful".
The parties aim to translate into a lasting accord a landmark interim deal struck in November under which Iran agreed to freeze certain activities for six months.
This was in exchange for minor relief from sanctions causing the Iranian economy major damage and for a promise of no new EU or Western sanctions.
The six months expire on July 20 but can be extended, with the parties aiming to conclude negotiating and commence implementing the final "comprehensive" deal by November.
Iranian Foreign Minister Mohammad Javad Zarif said late Tuesday that the talks in Vienna with the United States, Russia, China, Britain, France and Germany had "started on the right track".
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"We have a shared objective, and that is for Iran to have a nuclear programme that is exclusively peaceful," he said from Vienna in a webcast discussion with Denver University's Center for Middle East Studies.
He said a deal was "totally achievable" but would take more than "one or two sittings" and would require "some innovation and some forward thinking".
Others have been considerably more circumspect about the prospects for a deal that satisfies hardliners on both sides, as well as other countries such as Israel, after a decade of failed initiatives and rising tensions.
Iran's supreme leader Ayatollah Ali Khamenei said on Monday that this effort would "go nowhere" but that he was not against trying.
"It is probably as likely that we won't get an agreement as it is that we will," said one senior US administration official.
"But these negotiations are the best chance we have ever had."
Iran has long been suspected of seeking atomic weapons, despite its denials, and the US and Israel -- the latter assumed to have a large atomic arsenal itself -- have never ruled out military action.
The aim of this first meeting in Vienna, tentatively scheduled to finish Thursday, is merely to develop a "workable framework to facilitate these negotiations" in future rounds, Mann said.