Geneva: Iran nuclear talks enter their critical end-game Sunday with US Secretary of State John Kerry due to meet his Iranian counterpart in Switzerland as a March 31 deadline looms and a political storm rages in Washington.
After 18 months of talks and two missed deadlines, six world powers want by the end of the month to nail down the outline of a deal with Iran that would put making a nuclear bomb out of Tehran`s reach.
A full accord is due by July 1. But as time runs short tempers have been boiling over in the United States, putting Kerry and US President Barack Obama under immense pressure.
Iran`s supreme leader, Ayatollah Ali Khamenei, has meanwhile criticised the two-step process, saying matters should be handled in one fell swoop. He is due to give a closely watched Iranian New Year`s address on March 21.
On Thursday Khamenei said the other side in the talks is "deceitful and stabs in the back," according to news agency ISNA.
From Lausanne, Iranian Foreign Minister Mohammad Javad Zarif is due to go to Brussels on Monday to meet his French, German and British counterparts before returning to Switzerland, according to his ministry.On March 9, 47 Republican US senators wrote an open letter to Iran`s leaders warning that any nuclear deal could be modified by Congress or revoked "with the stroke of a pen" by Obama`s successors.
This followed an address to US lawmakers -- on a Republican invitation -- by Israeli Prime Minister Benjamin Netanyahu when he warned that the mooted deal would leave Iran`s nuclear programme "largely intact".
Obama said that it was "somewhat ironic to see some members of Congress wanting to make common cause with hardliners in Iran". Kerry called the missive "irresponsible".
And German Foreign Minister Frank-Walter Steinmeier, whose country is one of the six powers in the talks, said Iran was increasingly sceptical as to "whether we are really serious".
Zarif, who together with reformist President Hassan Rouhani is also under pressure from their own hardliners, was scathing about the letter from US "extremists", saying it had "no legal value".
"In truth, it told us that we cannot trust the United States," Zarif told top clerics.The deal being sought would involve Iran agreeing to shrink its activities to extend to at least a year the "breakout time" that Iran would, in theory, need to assemble a bomb`s worth of fissile material.
Iran, saying its nuclear activities are purely for peaceful purposes, wants in return the lifting of painful UN and Western sanctions imposed over the last decade.
In November 2013, Iran and the "P5+1" powers -- the US, Russia, China, Britain, France and Germany -- agreed an interim accord involving a partial nuclear freeze by Iran and minor sanctions relief.
After numerous rounds of talks since, negotiators twice failed to turn this into a lasting deal by two self-imposed deadlines of July and then November of 2014, extending instead the interim arrangements.
Diplomats say there has been progress in some areas, including changing the design of the Arak reactor that could give Iran weapons-grade plutonium once operational.
EU foreign policy chief Federica Mogherini said on March 6 a "good deal is at hand".
But the key issue of the future scale of Iran`s uranium enrichment capacities -- producing nuclear fuel but also potentially bomb material -- remains unresolved.
Other thorny topics involve the pace at which sanctions would be suspended and eventually lifted and the duration of the mooted accord. France believes the 10 years suggested in some quarters is not enough.
"If we cannot verify that they are not going to obtain a nuclear weapon, that there`s a breakout period so that even if they cheated we would be able to have enough time to take action -- if we don`t have that kind of deal, then we`re not going to take it," Obama said in a TV interview aired on March 8.