Iran entrenched its position at nuclear talks in Geneva on Thursday, insisting it would not sign an agreement that did not have specific guarantees of its right to enrich uranium.
The talks adjourned for the night, with no sight of a breakthough. Iran's deputy foreign minister, Abbas Araqchi, said: "We are working on narrowing the gaps, but the gaps are still there."
Western officials said that Iran's right to enrich was one of the most serious of those gaps.
The issue is one of the thorniest at the negotiations and one of the main reasons the last round of talks here broke up without agreement on 10 November despite intense bargaining by ministers including the US secretary of state, John Kerry, and his Iranian counterpart, Mohammad Javad Zarif.
This week Zarif appeared to offer a concession, suggesting Tehran might no longer insist on hammering out wording in the interim agreement that explicitly guaranteed Iran the right to enrich uranium, saying there could be references to the right already, under the nuclear non-proliferation treaty.
But an Iranian negotiator at the talks denied the Iranian position had eased. "If this element is not in the text, it is unacceptable to us. Without that, there will be no agreement."
The 1968 NPT is vague on the subject. It guarantees a nation's right to a peaceful nuclear programme, without mentioning enrichment specifically. But signatories are obliged not to develop weapons and to agree on inspection regimes with the International Atomic Energy Agency (IAEA).
A compromise had been floated in the days running up the latest Geneva talks whereby the agreement text would mention NPT rights and the parties would interpret that in their own way. However, the Iranian negotiator said that would not be enough for Tehran. "It is because there are different interpretations of the NPT that there is a need to spell it out in the text. We are trying to find language that is the least problematic for all parties, but what is essential is the element of enrichment."
Western states acknowledge that they will have to accept some degree of Iranian enrichment as a fait accompli in any interim agreement. This is the focus of the Geneva agreement being negotiated, a deal that aims to slow down, stop or reverse elements of the nuclear programme in exchange for limited sanctions relief.
However, Washington and its allies, particularly France, do not want to put that acceptance in writing, lest it serve as a legal precedent for global proliferation. Enrichment of uranium is a dual-use technology which can produce weapons-grade fissile material for warheads as well as fuel for nuclear power stations.
The Iranian official at the talks said he had not read Zarif's earlier, apparently conciliatory, remarks on enrichment.
Western officials at the talks said the Iranian delegation had stressed how much pressure they had been under at home from hardliners. Iran's supreme leader, Ali Khamenei, declared on the eve of the new round of talks in Geneva that the negotiators had been set strict red lines on what they could accept.
Zarif met the EU foreign policy chief, Catherine Ashton, on Thursday morning for detailed talks on the current draft agreement, which has disputed paragraphs in brackets, and negotiators said the general atmosphere was positive.
Contingency preparations have been made for Kerry and foreign ministers from the other five nations at the talks – the UK, France, Germany, Russia and China – to fly to Switzerland at short notice if a deal is near.
Araqchi said that if the remaining gaps in the negotiations narrowed, the foreign ministers would probably fly in.
However, France signalled on Wednesday that it would stick to its tough line on Iran and that it was not ready to make more concessions.
Laurent Fabius, the French foreign minister, said he hoped a deal could be clinched but added: "This agreement can only be possible based on firmness. For now, the Iranians have not been able to accept the position of the six. I hope they will accept it."
The Iranian official said that in contrast to the last round of talks, when Fabius openly voiced objections to a draft text, the six-nation group had stayed united on this occasion and let Ashton talk on their behalf. "The French are no longer in the forefront of negotiations," he said.
