Tortuous negotiations aimed at ending fears that Iran will acquire nuclear arms shifted into top gear Saturday, with the Iranian foreign minister saying he was confident the outstanding hurdles blocking a deal could be overcome.
"We're moving forward," Iranian Foreign Minister Mohammad Javad Zarif told reporters after meeting separately with his German and French counterparts, who he said were both "serious" about reaching an agreement.
"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 that will become the final agreement once it's done," Zarif said as the clock ticked down to Tuesday's deadline for the broad outlines of a deal.
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" any deal included mechanisms to ensure that the Islamic republic, which denies wanting nuclear weapons, complies with its commitments, he said.
Asked later after meeting Zarif and separately with top US diplomat John Kerry if progress was being made, Fabius said: "We're working, we're working. We're trying to make progress."
German Foreign Minister Frank-Walter Steinmeier also arrived in Lausanne saying the talks had entered their "endgame" after 12 years, but warning also this would also be the hardest stage.
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 whether they were expecting a good day, Kerry replied wryly that "we're expecting an evening today," while Zarif joked "evening, night, midnight, morning."
The EU's foreign policy chief Federica Mogherini confirmed she would be arriving in Lausanne later Saturday. China's Foreign Minister Wang Yi and Russian counterpart Sergei Lavrov will reportedly fly in on Sunday. Britain's Philip Hammond is on stand-by.
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.
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, like US ally Israel, 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.
"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."