has warned that difficult issues remain in the way of securing a deal on Iran's nuclear programme as he joined foreign ministers from major world powers for talks in Geneva.
The British foreign secretary said that he and his counterparts from the US, France, , Russia and China had come together to try overcome the last sticking points, not because there was already a deal to sign.
The negotiations remain stuck on "the same areas of difficulty" that stymied a breakthrough agreement at the last round of negotiations a fortnight ago.
"The foreign ministers have come to support these negotiations and to be able to confer together easily and quickly if we need to make fresh decisions of any kind," Hague said. "They remain difficult negotiations. I think it's important to stress that. We're not here because things are necessarily finished. We're here because they're difficult."
Those areas of difficulty are known to include disputes between western states and Iran over how far a written agreement should endorse Iran's right to enrich uranium, and how far a stopgap deal should go to shut down construction work on a heavy water reactor is building in Arak.
"They are narrow gaps but they are important gaps, and its very important that any agreement here is thorough, that it is detailed, that it is comprehensive, and that its a deal in which the whole world can have confidence that it will work," Hague added.
"The same areas of difficulty remain," Hague said. "That means there are many areas of agreement. There is a huge amount of agreement and it remains the case that there has been a huge amount of progress being made in recent weeks."
The US secretary of state, , and his French and German counterparts, Laurent Fabius and Guido Westerwelle, arrived earlier on Saturday. The Russian foreign minister, Sergei Lavrov, flew in on Friday and his Chinese opposite number, Wang Yi, is expected later on Saturday. Iran is represented by its foreign minister, Mohammad Javad Zarif, and the talks are chaired by the EU foreign policy high representative, Catherine Ashton.
The same ministers took part in the Geneva talks two weeks ago but fell short of a deal despite three days of intense and complex negotiations.
After arriving at dawn, Kerry held meetings with Ashton, Fabius and Lavrov, in an effort to maintain a common front among the six nations mandated by the UN security council to handle the negotiations.
At the previous round which ended on 10 November, differences among the western states, with insisting on a tougher line than its allies, complicated the talks.