Iran and six world powers still have a long way to go in overcoming their differences over Tehran's uranium enrichment programme, though all parties aim to adhere to their six-month deadline to reach a nuclear deal, a senior US official has said.
"It's a gap [on enrichment] that's going to take some hard work to get to a place where we can find agreement," the senior US administration official said after the latest round of negotiations on Iran's atomic programme in Vienna.
The official said there were many elements involved in Iran's enrichment activity that would need to be settled, including monitoring, the Natanz and Fordow enrichment facilities, and Iran's stockpiles of the material, the Reuters news agency reported without giving the source's name.
Iran also said on Wednesday that more time was needed to hammer out a permanent nuclear agreement.
"It is too early to enter into negotiations for drafting a text for a final agreement," senior Iranian negotiator Abbas Araqchi was quoted as saying by the ISNA news agency.
"Everybody has some work to do to follow up on that discussion," the US official said, adding that Britain, China, France, Germany, Russia, the US and Iran all hoped to honour the late-July deadline they set in November for a long-term nuclear deal between the six powers and Iran.
That deadline was agreed as part of an interim deal reached in November under which Iran froze some parts of its atomic programme in exchange for limited sanctions relief.
The official's comments came as Catherine Ashton, the European Union foreign policy chief, and Mohammad Javad Zarif, the Iranian foreign minister, told reporters in Vienna that they had held "substantive" and "useful" talks, and that they would meet again on April 7-9 in the Austrian capital.
"We had substantive and useful discussions covering a set of issues including [uranium] enrichment, the Arak reactor, civil nuclear cooperation and sanctions," Ashton said.
The differences over Iran's planned Arak heavy-water reactor, which Western powers fear could yield weapons-grade plutonium, remained similarly wide, the US official said. Iran says the reactor it is for peaceful medical purposes.
"We all understand Arak and what it is and how it operates, what its technical requirements are in ways that we did not
before," the official said.
"We got some very detailed information. Likewise we shared with Iran ideas that we had. You know what our concerns are about Arak. We shared with Iran ideas that we have," the senior official added.
"We have long said that we believe that Arak should not be a heavy water reactor as it is, that we did not think that that met the objectives of this negotiation. And so of course we are having discussions about how to address that."
Without giving details, the official added that "there are many options" for Arak. One option, the US has previously suggested, is converting it to a light-water reactor, a model less amenable to producing bomb material.
Zarif told reporters "the Arak reactor is part of Iran's nuclear programme and will not be closed down". However, he did not explicitly rule out modifying the reactor to allay concerns about the facility.
Tehran is under US, EU and UN sanctions for refusing to suspend enrichment and other sensitive atomic activities that it says are intended for civilian purposes only.