Iran nuclear deal framework 'agreed' in Vienna
Iran has said talks with world powers on its nuclear programme have concluded with agreement on a framework for negotiations on a comprehensive deal.
Deputy Foreign Minister Abbas Araqchi told state media there was a "positive atmosphere" at the summit in Vienna.
EU foreign policy chief Catherine Ashton said representatives identified the issues that needed to be resolved.
But she cautioned that there remained a "lot to do" and it would not be easy to build on November's interim agreement.
The deal with the so-called P5+1 - the US, UK, France, China and Russia plus Germany - saw Iran curb uranium enrichment in return for partial sanctions relief.
The world powers want Iran to scale back its sensitive nuclear activities permanently to ensure that it cannot assemble a nuclear weapon.
But Iran says its nuclear work, which it insists is peaceful, will continue - and wants an end to the sanctions that have crippled its economy.
After two days of meetings chaired by Baroness Ashton in the Austrian capital, Mr Araqchi told the Iranian state news agency that both sides had "reached an agreement on the framework and plan of action for the comprehensive nuclear talks".
"The negotiations took place in a positive atmosphere, but we still cannot be optimistic about the progress of the upcoming talks," he added.
In a statement, Baroness Ashton said: "We have had three very productive days during which we have identified all of the issues we need to address in reaching a comprehensive and final agreement.
"There is a lot to do. It won't be easy but we have made a good start."
She added that the next round of talks would take place in Vienna on 17 March, and that technical experts had also begun discussions.
The interim deal, which was struck in November but only took effect on 20 January, gives both sides six months to negotiate a comprehensive solution, although that deadline can be extended.
The agreement obliges Iran to halt production of near-20% enriched uranium, which could be further enriched to weapons-grade relatively quickly; dilute half of its stockpile; commit not to commission or fuel the Arak heavy water reactor, from where spent fuel plutonium could be extracted; and submit to daily inspections by the International Atomic Energy Agency (IAEA).
In return, the P5+1 has eased sanctions on trade in petrochemicals, precious metals and on the provision of insurance for oil shipments. It has also committed to give Iran access to $4.2bn of oil revenue frozen in foreign banks at monthly intervals.
The issues for the permanent deal are said to include the level of Iran's ongoing enrichment of uranium; the underground enrichment facility at Fordo; the Arak reactor; and Tehran's willingness to let inspectors visit the Parchin military complex, where the IAEA suspects activities "relevant to the development of a nuclear explosive device" have been carried out.
Iran has a number of "red lines", including not dismantling any facilities.