Iran's foreign minister says he believes 'ingredients are there' for historic breakthrough after decade of diplomatic sparring

Iranian and western officials will start drafting a nuclear agreement in Geneva on Friday after international negotiations made dramatic progress, Iran's foreign minister has told the Guardian.

As hopes of a breakthrough soared, the US secretary of state, John Kerry, is to travel to Switzerland on Friday to help seal an agreement which could, if successful, go a long way towards defusing tensions in the Gulf and put off the threat of new war in the Middle East.

A senior US state department official said: "Secretary Kerry will travel to Geneva, Switzerland, on Friday at the invitation of EU high representative Ashton in an effort to help narrow differences in negotiations."

It was not clear if his British counterpart, William Hague, was also considering attending the talks.

Speaking during a break in the talks, Iran's foreign minister, Mohammad Javad Zarif, said it was quite possible that the agreement would be finished by the end of Friday, but that much would rely on the contribution of western diplomats.

"Depending on what they put on paper with us, we can decide whether it's a major deal or a small step in the right direction. I hope its more than a small step in the right direction, but I'll be happy if we move in the right direction," Zarif said.

An agreement on any scale would represent a historic breakthrough after a decade of diplomatic sparring marked by paralysis and distrust.

Zarif said the process of drafting would begin on Friday morning at a meeting with the EU foreign policy chief, Lady Ashton, who acts as a convenor for the six world powers with delegations in Geneva: the US, UK, France, Germany, Russia and China.

"I believe the ingredients are there. I believe there is a general understanding of everyone involved, but it is important at the same time to start doing things in black and white and try to move forward with the text," Zarif said.

The two days of talks in Geneva brought together Iran and six global powers to discuss the future of Iran's nuclear programme. Western officials agreed that drafting work could begin on Saturday, but cautioned that there were still many difficult issues to resolve.

Zarif said the six other nations in Geneva had agreed to Iran's initial multi-phase plan: a statement of intent encompassing an initial confidence-building measure as a first, and an outline of the ultimate goal of a comprehensive agreement on Iran's nuclear programme and normalisation of relations between Tehran and the west.

The foreign minister said negotiations had gone further in the first day than agreeing a framework. "We have gone beyond that and we have agreed on the elements that have to be incorporated in each one of these [steps]. The manner in which we incorporate them and the balance we strike between these elements – that's the sort of question we have to answer tomorrow," he said.

It is widely expected that both an interim deal and a longer-term settlement would involve western acceptance of Iran's enrichment programme in return for Iranian acceptance of limits on its scope, particularly a cap on the level to which it could enrich uranium of about 5%, sufficient for fuel for nuclear power stations.

There would also have to be an agreement on how far Iran could go in developing a heavy-water reactor at Arak, which would produce plutonium, and on Iranian acceptance of extensive and intrusive inspections by the international watchdog, the International Atomic Energy Agency (IAEA).

As the negotiations proceeded in Geneva, the Israeli premier, Binyamin Netanyahu, warned against any agreement that left the Iranian nuclear programme in place. He said: "I believe adopting the proposals is a mistake of historic proportions. They must be rejected outright."

Asked about Netanyahu's comments, Zarif said: "I don't think he's an authority on mistakes because he's been making mistakes for his entire life. He's been calling the Iranian programme six months away from a nuclear weapon since 1991, so I don't consider him a credible authority."

On the reception a nuclear bargain is likely to receive in Iran, the foreign minister said: "It depends on the type of deal that we get. The Iranian public is very sceptical about the process and I believe rightly so because we haven't had a very positive experience in the past.

"What is important is to prepare a solid agreement that all sides can be happy with and all sides can sell to their populations. For Iran, because it is our right. Its our programme, it is important that it is respectful and based on equal footing, and I believe we can sell it to the public. If we can't, I don't think we should agree to it."

Zarif is not the only participant in the Geneva talks likely to face resistance back home. In Washington on Thursday, the US Senate said it would move ahead with a debate on tough new sanctions on Iran after the Geneva meeting was over. Some senators have said they would consider loosening the sanctions regime, but only in return for dramatic concessions from Tehran.

In another sign of progress, Zarif said the head of the IAEA, Yukiya Amano, would visit Tehran on Monday, raising expectations of a breakthrough in long-running talks between the Iranian government and the agency aimed at clearing up uncertainty over Iran's past development work on nuclear weapons.

Zarif said: "Mr Amano's visit is going to be an important indication that we are in process in moving forward."

His optimistic remarks followed a full meeting of all the delegates and then separate discussions between Iranian officials with diplomats from the US, Russia and China, and one with representatives of the three European states.

British and Iranian diplomats discussed the eventual appointment of non-resident chargés d'affaires in each other's countries.

Zarif had cancelled a trip to Rome so that he could hold a face-to-face meeting with Ashton as it became clear that substantial progress was being made.

"In response to a first step agreed to by Iran that halts their programme from advancing further, we are prepared to offer limited, targeted and reversible sanctions relief," a senior US official said before the talks began. "We are not talking about touching the core architecture of the Iranian sanctions regime in this first step in any way. And if Iran does not live up to its obligations under the initial understanding, or if we cannot get a comprehensive agreement finalised, any economic relief we will have given Iran can, in fact, be reversed."

Issues to be resolved

• Iran's right to enrich uranium as part of its nuclear programme

• The limits to enrichment. Likely to be under 5% – enough to fuel nuclear power stations

• Future of the heavy water reactor being built in Arak, which could produce plutonium

• Iran's agreement to the IAEA additional protocol, which involves more intrusive nuclear inspections

• Iran's stockpile of medium-enriched (20%) uranium, which could be turned into reactor fuel so that it would be less of a proliferation risk.

• Possible caps on the amount of low enriched uranium produced or on the number and efficiency of centrifuges

• Fate of the underground enrichment plant at Fordow – whether it should be closed and mothballed or simply placed under intense monitoring.