Lausanne (AFP) - Tortuous negotiations aimed at laying to rest fears that Iran will acquire nuclear weapons shifted into top gear Saturday with each side demanding the other give ground ahead of a looming deadline.
"We're at that point in the negotiations where we really need to see decisions being made," a senior US State Department official said late Friday at the talks in Switzerland.
"The work is very complicated and difficult. The other side needs to choose between pressure and a political accord," countered Iranian Foreign Minister Mohammad Javad Zarif.
France's top diplomat Laurent Fabius, the most hawkish in the P5+1 group of countries negotiating with Iran since late 2013, was the first European minister to fly in for the crucial talks saying he wanted to reach a "robust deal".
France was "insisting" that any deal included mechanisms to ensure that the Islamic republic, which denies wanting nuclear weapons, complies with its commitments, he said Saturday.
German Foreign Minister Frank-Walter Steinmeier arrived in Lausanne soon afterwards, saying that the talks had entered their "endgame" after 12 years but that this would also be the hardest stage.
Fabius and Steinmeier joined US Secretary of State John Kerry, Zarif and negotiators from the six powers, chasing an agreement on the broad outlines of what they hope will be a historic deal by Tuesday.
Since a major diplomatic push to resolve the long-running crisis began in 2013, Kerry and the US-educated Zarif have met multiple times, but have twice missed a deadline to nail down an accord.
The powers want Iran to shrink its nuclear programme in order to make it easy to detect any dash to make a bomb under the guise of its civilian atomic programme.
In return, Iran wants an easing of international sanctions that have excluded the Islamic republic from lucrative oil markets and crippled its economy.
- Pulling an all-nighter? -
Asked at the start of their talks Saturday morning whether they were expecting a good day, Kerry replied wryly that "we’re expecting an evening today," while Zarif joked "evening, night, midnight, morning."
China's Foreign Minister Wang Yi and Russian counterpart Sergei Lavrov will reportedly fly in on Sunday, as well as the EU's foreign policy chief Federica Mogherini. Britain's Philip Hammond was on stand-by to come.
Kerry, Fabius and Steinmeier will have a working lunch Saturday, a US official said.
The emerging accord is to be rounded out with complex technical annexes by a June 30 deadline, and Iran's nuclear chief Ali Akbar Salehi said he was busy redoing his "technical calculations".
World powers want to ensure that any deal will result in a year-long "breakout time" -- the amount of time needed for Iran to covertly gather enough fissile material to be able to make a bomb -- and experts say there are several routes to getting there.
"Everything is linked. If all the technical issues are resolved and the questions tied to the sanctions are not, then there is no deal," Salehi said.
Iran wants the sanctions lifted immediately but global powers insist on a gradual phasing out of sanctions in case Iran violates the deal.
The UN has imposed several rounds of sanctions since 2006 aimed at stopping Iran from expanding its nuclear and missile programmes while EU and US sanctions since 2010 have targeted its oil exports and financial system.
It remains unclear what form any deal to emerge from the Lausanne talks would take. Iran's Deputy Foreign Minister Abbas Araghchi told reporters on Saturday morning that "no text has been prepared".
Kerry is under pressure to return from Lausanne with something concrete to head off a push by Republican lawmakers to introduce yet more sanctions, potentially torpedoing the whole negotiating process.
The Republicans are concerned that by leaving some of Iran's nuclear infrastructure intact, as seems likely, the mooted deal will not do enough to prevent Iran getting the bomb.
This concern is shared by Israel, widely assumed to have nuclear weapons itself, as well as Saudi Arabia, worried by the prospect of any US-Iranian rapprochement with the West after 35 years of acrimony.
"A deal is possible, but Iran will have to make painful choices," a Western diplomat said, adding however that "the Iranians like to negotiate on the edge of a precipice. They're very good at it."