Iran's president today appealed to the leaders of Britain, France and Russia to seize an "exceptional opportunity" to strike a nuclear deal, as negotiators raced against the clock in Switzerland.
"We are acting in the national and international interest and we should not lose this exceptional opportunity," Hassan Rouhani told British Prime Minister David Cameron by phone, the presidency said.
Rouhani, whose 2013 election led to the biggest effort in years to end the decade-old standoff over Iran's nuclear activities, also spoke to Russian President Vladimir Putin and France's Francois Hollande.
"Hope was expressed for success at the new round of talks in Lausanne," the Kremlin said in a statement, while noting with "satisfaction the progress" made over previous weeks of talks.
Hollande, "while insisting on Iran's legitimate right to use peaceful nuclear power, insisted on the need to work towards a lasting, robust and verifiable agreement," the French presidency said.
"The peaceful character of (Iran's) nuclear activities and the necessity to annul all the unjust sanctions can lead us to a final deal," Rouhani's office quoted him as telling Cameron.
The six powers negotiating with Iran -- the United States, China, Russia, Britain, France and Germany -- are however insisting that sanctions will only be suspended, not lifted.
This, they say, is to enable the sanctions to be "snapped back" if Iran violates the deal. The suspension will also be staggered over a number of years and tied to certain actions by Iran.
Kerry's talks in Lausanne with Foreign Minister Mohammad Javad Zarif and officials from the six powers are aimed at agreeing the outlines of a nuclear deal by March 31 after two missed deadlines in 2014.
The two men met for more than four hours today, and their political directors were planning to resume talks later in the evening.
Such a deal, meant to be finalised by June 30, would see Iran downsize its nuclear programme to ensure that any covert dash for an atomic weapon would be all but impossible.
Kerry is under severe pressure from the US Congress to return from Lausanne with something concrete but it is unclear how detailed any "framework" accord will be, or even whether it will be a written document.