World-power foreign ministers were due today to make a final push to get Iran to agree to curtail its nuclear programme days before a looming deadline to agree the outlines of a deal.
On Saturday officials expressed guarded optimism that after 18 months of tortuous negotiations and two missed deadlines a breakthrough might be in sight for a deal ending 12 years of tensions.
"We're moving forward," Iranian Foreign Minister Mohammad Javad Zarif, hunkered down with US Secretary of State John Kerry in Switzerland since Thursday, told reporters.
"I think we can in fact make the necessary progress to be able to resolve all the issues and start writing them down in a text," Zarif said.
German Foreign Minister Frank-Walter Steinmeier, who like French counterpart Laurent Fabius joined the negotiations on Saturday, said the talks were in the "endgame".
Steinmeier added however that "the final metres are the most difficult but also the decisive ones".
Russia's chief negotiator, Sergei Ryabkov was quoted by the RIA Novosti news agency as saying the chances of a deal were "more than 50/50".
EU foreign policy chief Federica Mogherini, who arrived late Saturday, said negotiators "have never been so close to a deal" but added there remained "critical points" to resolve.
Russian Foreign Minister Sergei Lavrov and China's Wang Yi were reportedly due to join the talks on Sunday. Britain's Philip Hammond was also expected, completing the line-up.
A senior US State Department official said that she expected the presence of all foreign ministers in Lausanne would allow "the pace to intensify".
The mooted deal, due to be finalised by June 30, would see Iran scale down its nuclear programme and allow unprecedented inspections of its remaining activities.
