GENEVA // A senior Iranian official raised doubt on Saturday whether an agreement to curb Iran’s nuclear programme could be finalised during current talks in Geneva after a day of intense diplomacy joined by the US secretary of state John Kerry and five other foreign ministers.

The Iranian deputy foreign minister Abbas Araghchi told Iran’s Fars news agency that the bargaining was primarily over the wording of a draft six-month agreement that would offer Iran limited relief from economic sanctions in return for curbs on its nuclear programme.

But Mr Araghchi also said it was unclear whether the differences could be ironed out on Saturday – the fourth day of what was supposed to have been two days of talks.

US officials insisted Mr Kerry would stick by plans to leave on Sunday for talks in London. That raised the possibility that another session may have to be scheduled.

The goal is to hammer out an agreement to freeze Iran’s nuclear programme for six months while offering the Iranians limited relief from crippling economic sanctions. If the interim deal holds, the parties would negotiate final-stage agreements to ensure Iran does not build nuclear weapons.

Only then would the most crippling sanctions on Iranian oil sales and financial transactions be rolled back.

The talks have been difficult not only because of the complex issues but also deep misgivings on each side about dealing with the other.

The Iranians, mindful of opposition to any restrictions among hardliners back home, have insisted on retaining the right to produce nuclear fuel by enriching uranium, saying they need it to produce electricity and for scientific research.

They also are holding out for maximum relief from sanctions hurting their economy, while the United States and its allies want to relax sanctions in small, incremental steps. Even those have not set well with Israel or some members of Congress.

Talks on Saturday appear to have included ways Iran could retain some level of enrichment, albeit at a level far below what’s need for weapons. Other roadblocks were believed to include the level of sanctions relief and the future of a plutonium reactor under construction at Arak that the six want closed. Plutonium can also be used to make weapons.

Mr Kerry and his counterparts from Russia, Britain, France, China and Germany joined the Geneva talks after Iran’s foreign minister, Mohammed Javad Zarif, and the top European Union diplomat, Catherine Ashton, reported progress on enrichment and other issues on Friday.

Their participation raised speculation that an agreement was close – an interpretation that the foreign ministers themselves sought to discourage.

William Hague, the British foreign secretary, spoke of “very difficult negotiations”, over issues that blocked agreement at the last round this month.

“We’re not here because things are necessarily finished,” Mr Hague told reporters. “We’re here because they’re difficult, and they remain difficult.”

Among the key stumbling blocks, uranium enrichment is especially sensitive. Iran insists it has no interest in nuclear weapons but needs to enrichment to generate electricity and for scientific and medical purposes.

Washington and its allies are sceptical because of Tehran’s earlier efforts to hide enrichment. Israel, which is not a party to the talks, opposes allowing any Iranian enrichment capability.

Iran has suggested it could curb its highest-known level of enrichment – at 20 per cent. But critics worry that Iran could ramp up to weapons grade enrichment quickly if the 20 per cent threshold is allowed to remain.

* Associated Press