John Kerry acknowledges 'tangible progress' in nuclear talks with Iran

The top diplomats from the US and Iran have hailed the progress made so far at nuclear talks in Vienna but say more time may be needed to close the remaining gaps between the sides.

The US secretary of state, John Kerry, said on Tuesday that there had been tangible progress after two days of face-to-face negotiations with his Iranian counterpart, Mohammad Javad Zarif.

Zarif told reporters: "As we stand now, we have made enough headway to be able to tell our political bosses that this is a process worth continuing. This is my recommendation. I am sure secretary Kerry will make the same recommendation."

Sunday is the deadline for a comprehensive agreement to be completed, but it can be extended with the agreement of all sides at the Vienna talks.

Kerry said the negotiations were being carried out "in good faith" on both sides but there were still "very real gaps" that had to be closed. He said the July 20 deadline was still on the table and flew back to Washington to consult President Barack Obama and Congress on progress so far and the next steps.

"It is really important for Kerry to bring a product home so he can sit in front of the senate committee on foreign relations and say progress is being made, and stop Congress imposing new sanctions," said Ellie Geranmayeh, a policy fellow at the European Council on Foreign Relations.

Geranmayeh said a formal extension to the talks could involve a separate negotiation in which Iran could demand more sanctions relief. Another option would be for the negotiators simply to carrying on through the Sunday deadline for however many days or weeks it takes to clinch a deal.

Speaking to the press, Kerry refused to be drawn on details of the negotiations, saying he would not bargain in public. But he stated firmly that Iran's current capacity for uranium enrichment, of 19,000 centrifuges, was too much.

Overnight, Zarif gave an interview to the New York Times (NYT) in which he said Iran was willing to freeze its enrichment capacity for up to seven years on the condition it would then be free to operate without any special restrictions.

Western states want Iran's uranium enrichment capacity reduced, and then frozen in place for at least 10 years, and they have a long list of conditions Iran would have to fulfil over the long term before it would be allowed to function as any other state with a civilian nuclear energy programme.

However the Zarif offer, if confirmed, suggests there is enough flexibility on the Iranian side at least to gain extra time for the talks beyond the deadline, which the negotiating states imposed on themselves. "I'm not here to present maximalist positions," Zarif said. "We're here to reach an agreement."

In his remarks, Kerry went out of his way to compliment Zarif as "a tough negotiator". He seemed to appeal directly to Iran's supreme leader, Ali Khamenei, by saying that the US took his fatwa, or religious edict, against nuclear weapons very seriously, but that such a declaration had to be codified and verifiable to be turned into an agreement.

Iran currently has 19,000 centrifuges in two enrichment plans, of which about 9,000 are in operation. The US and the other five sides involved in the Vienna negotiations – the UK, France, Germany, Russia and China – would like that number reduced so that it would take Iran longer, if it took the decision to build a weapon, to expel international inspectors and make a dash to make a bomb.

The west would like this theoretical breakout time to be over six months and preferably a year. Zarif said other conditions could be inserted into a deal that would give extra assurances to the international community that Iran could not make a nuclear weapon quickly.

All the low-enriched uranium produced by the centrifuges would be turned into oxide, suitable for reactor fuel, and Iran would not build the facility necessary to turn that oxide back into gas, the state it needs to be in to be enriched further, to weapons-grade uranium.

What is not clear is what conditions Iran would have to fulfil in order to be treated like other countries that have a nuclear energy programme, free of sanctions and special restrictions. Kerry has listed some of the conditions the US is setting, including a seal of approval from the International Atomic Energy Agency that Iran has answered all the questions its inspectors have about evidence of weapons development work. Iran would also have to sign the IAEA "additional protocol" which allows for enhanced inspections. There would also be pressure on Tehran to carry out uranium enrichment as part of a regional consortium, to prevent a proliferation of enrichment technology across the Middle East.

When asked by the NYT for a response to Zarif's offer, a senior US official said: "We have consistently said we wouldn't negotiate in public, and we're not going to start doing so now. Some of the things described in this interview they have put forward in negotiations. Some have not come up. And on some, they've shown more flexibility behind closed doors."