Vienna: US Secretary of State John Kerry arrived in Vienna Sunday to face off with Iranian counterpart Mohammad Javad Zarif, seven days before a deadline to strike a historic but elusive-looking deal on Tehran`s suspect nuclear programme.
Kerry and the foreign ministers of Britain, France and Germany also plan to use their presence in the Austrian capital to discuss an international push for a ceasefire in Gaza.
Fresh from brokering a breakthrough in Afghanistan to end its election crisis, Kerry will also seek to ease a major row over spying with Germany, which saw the CIA chief in Berlin expelled from the country.
Iran`s talks with the five permanent members of the UN Security Council plus Germany are aimed at a grand bargain to reduce the scope of Iran`s nuclear activities in return for sanctions relief.
Such a deal is meant to quash for good concerns about the Islamic republic getting the bomb after a decade of failed diplomacy, threats of war and atomic expansion by Iran, which denies that its programme is aimed at acquiring nuclear weapons.
Iran`s chief negotiator warned on Saturday that Tehran was prepared to walk away from the talks and resume expanding its activities if "excessive" Western demands cause the negotiations to fail.
"If we see the excessive demands (of Western powers) persisting and that a deal is impossible, this is not a drama, we will continue with our nuclear programme," Abbas Araqchi told state television.
Officials on both sides say that the marathon talks, which on July 3 entered their sixth and final round, have made some progress, with Tehran saying that a draft accord was 60-65 percent completed.
But one thorny issue remains: uranium enrichment, a process which can produce nuclear fuel -- Iran`s stated aim -- but in highly purified can also form the core of an atomic weapon.
Iran wants to greatly increase its enrichment capacities, saying it needs them to feed its only functioning nuclear power plant -- currently fuelled by Russia -- and a fleet of future facilities.
But the six powers want a sharp reduction, saying that Iran has no need for such a large programme at present. Washington wants it limited for at least 10 years, a senior US official said Saturday.
Such a reduction, plus increased surveillance, would extend the so-called "breakout time" -- the time Iran would need to make enough highly-enriched uranium for a nuclear weapon, if it choose to do so.
"We have made some progress but on some key issues, Iran has not moved from their ... unworkable and inadequate positions", the senior US official said in Vienna.
Proposals on enrichment made by Iran behind closed doors in Vienna remain "far from a significant reduction," she said.In Vienna Kerry was due to meet EU foreign policy chief Catherine Ashton, lead negotiator for the six powers.
Absent however was Russian Foreign Minister Sergei Lavrov, although officials sought to play down any speculation of a rift with the other powers. It was unclear who was representing China.
Kerry`s aim in Vienna is to "assess Iran`s willingness to make a set of critical choices at the negotiating table," according to the State Department.
Many experts believe that if Kerry fails to get Iran to give ground he will recommend to US President Barack Obama that the July 20 deadline -- when a November interim deal expires -- be pushed back.
But with Obama facing accusations of weakness at home and pressure from Israel -- the Middle East`s sole if undeclared nuclear-armed state -- Washington has made clear it will not extend at any price.
"It will be hard to contemplate things like an extension without seeing significant progress on key issues," a second US official said Saturday.
"It is certainly late in the day in these negotiations, but it is not too late for Iran to take the steps that are necessary."