US Secretary of State John Kerry and his Iranian counterpart sought today to make progress in tortuous negotiations as the clock ticked down on reaching an elusive deal on Tehran's disputed nuclear programme.
A March 31 deadline loomed over Kerry and Mohammad Javad Zarif as they sat down for a second day of talks today, trying to agree the outlines of a deal that would bury any prospect that Iran might develop atomic weapons.
They hope that such an accord, which is meant to be finalised by July, would end a decade-plus standoff over the issue, with the West fearing that Iran is trying to develop nuclear weapons under the guise of a civilian programme, and Tehran denying the charge.
Yesterday, after Kerry, Zarif and others met for almost five hours in the lakeside Swiss city of Lausanne, a senior US official involved said that it remained uncertain whether the deal can be clinched.
"Iran still needs to make some very tough and necessary choices to address the significant concerns that remain about its nuclear programme," the official said on condition of anonymity.
"We're trying to get there. But quite frankly, we still do not know if we will be able to," the official said, likening the months of negotiations to a "rollercoaster".
After yesterday's meeting Zarif travelled to and from Brussels -- while Kerry went for a bike ride -- to meet European foreign ministers and EU foreign policy chief Federica Mogherini.
Political directors from the other five powers involved -- Russia, China, Britain, France and Germany -- are expected in Lausanne in the coming days, some as early as today.
The six powers want Iran to scale down its nuclear activities in order to extend the time Tehran would in theory need to make enough nuclear material for a bomb.
Critics in the United States and in Iran's arch foe Israel, widely assumed to have nuclear weapons itself, fear that the restrictions being proposed won't go far enough.
In Washington, a political storm is raging with 47 Republican senators last week writing to Iran's leaders telling them that Congress could alter any deal and that a future president could tear it up.
US President Barack Obama, a Democrat, is also fighting to stop the Republicans bringing new legislation that would force him to submit any deal to Congress for approval.
