Six world powers and Iran have began talks in pursuit of a final settlement on Tehran's contested nuclear programme, despite caution from both sides that a breakthrough deal may prove impossible.
Catherine Ashton, the European Union's top foreign policy official, met the Iranian foreign minister, Mohammad Javad Zarif, on Tuesday alongside representatives of the P5+1 Group, so-called because it comprises the five permanent members of the UN Security Council plus Germany.
|James Bays, Al Jazeera's diplomatic editor, reports from Vienna
At the start of the meeting in the Austrian capital Vienna, Abbas Araghchi, Iran's deputy foreign minister, declared that his country would not scrap any of its nuclear facilities, suggesting tough talks ahead.
But in an interview with Al Jazeera's James Bays, Araghchi later described the initial talks as a "positive meeting".
"He said it was very constructive," our correspondent said. "After that of course, this is going to be a very, very long negotiation."
This latest round of talks is aimed at finding a long-term agreement, following a short term agreement reached in November. The two sides have until July to find a permanent solution.
On Monday, Iran's Supreme Leader Ayatollah Ali Khamanei said he was pessimistic about talks, although he was not opposed to them.
"I have said before ... I am not optimistic about the negotiations. It will not lead anywhere, but I am not opposed either," Khamenei said during a visit to the Iranian city of Tabriz, according to the official news agency IRNA.
"What our foreign ministry and officials have started will continue and Iran will not violate its (pledge) ... but I say again that this is of no use and will not lead anywhere," Khamenei added.
A senior US official, speaking on condition of anonymity, said on Monday that the negotiation process would be complicated, long and have no guarantee of success.
"When the stakes are this high and the devil is truly in the details, one has to take the time to ensure the confidence of the international community in the result," the official said. "That can't be done in a day, a week or even a month in this situation."
Earlier this month, Iran agreed to an inspection of the Saghand uranium mine, as part of a seven-step plan with the International Atomic Energy Agency to ease international fears about its nuclear programme. The two sides reached agreement on seven practical measures to be implemented by Iran by May 15.
But Foad Izadi, from the University of Tehran, told Al Jazeera on Monday that there were two main points of contention regarding the talks and regarding the relationship between Iran and the US.
"There is a problem with rhetoric and there is a problem with enrichment. It's been a difficult issue since the beginning," he said. "Iran says article four of the non-proliferation treaty means it can enrich uranium in its own country, America disagrees."