Lausanne: Uncertainty reigned at crunch US- Iran nuclear talks on Tuesday as US officials warned that key differences remained but Tehran said that almost all technical issues were resolved ahead of a March 31 deadline for the outlines of a deal.
"We have agreed on 90 per cent of the technical issues," Iran's nuclear chief Ali Akbar Salehi was quoted by state television as saying from the marathon negotiations inside a plush hotel in the Swiss lakeside city of Lausanne.
"In most of the issues we have come to mutual agreements -- we have differences only in one major issue which we will try to solve in this evening's meeting" between Iran's Foreign Minister Mohammad Javad Zarif and US Secretary of State John Kerry, Salehi said.
The deal being sought by Kerry, Zarif and other negotiators including Salehi and US Energy Secretary Ernest Moniz will, they hope, convince the world that Iran will not develop nuclear weapons under the guise of its civilian programme.
The accord, due to be finalised by July, would involve Iran, which denies wanting the bomb, agreeing to scale down its nuclear activities to within strict limits in return for relief from sanctions suffocating its economy.
If they manage it and the accord holds, both sides hope it will end a 12-year standoff and potentially help normalise Iran's international relations at a particularly volatile time in the Middle East.
But it is highly complex, with both sides haggling over the adjustments to Iran's facilities needed to extend the "breakout" time to at least a year that Tehran would -- in theory -- need to process a bomb's worth of nuclear material.
At the same time both sides need to agree a timetable of relief from the spider's web of UN, US and EU sanctions imposed in recent years, tied to certain "milestones" and staggered over whatever duration the accord will have.
As a result US negotiators in the marathon talks were more downbeat, with one senior administration official -- involved in the technical side of the negotiations -- saying today there was still "a ways to go".
The official said on condition of anonymity that, specifically concerning technical dimensions, "even in this space we still have some tough issues to address."
A second US official said yesterday that "this is a Rubik's Cube or a puzzle ... And until all the pieces click into place, you don't have the whole picture, since this is all interlocking elements that affect each other."
Zarif and Kerry held almost five hours of talks yesterday before Zarif went to and from Brussels -- while Kerry went for a bike ride -- to meet European foreign ministers and EU foreign policy chief Federica Mogherini.
Zarif and Kerry were met again today. Political directors from the other five powers involved -- Russia, China, Britain, France and Germany -- began arriving in Lausanne today and were due to meet tomorrow, the EU said.