Negotiations over Iran's nuclear programme appeared to be on the cusp of an historic agreement on Sunday. The agreement, if finalised, would enable restrictions on Tehran's atomic energy production in exchange for relief from crippling sanctions imposed by US and other parties.
After more than two weeks of intense and often combative talks that blew through three deadlines in Vienna and a weekend of deadlock, diplomats expressed optimism that a deal was at hand.
US secretary of state John Kerry, who on Thursday had threatened to walk away from the negotiations, noted that "a few tough things" remain in the way of agreement but added, "We're getting to some real decisions".
En route to Mass at Vienna's gothic St Stephens Cathedral, Kerry said twice he was "hopeful" after a "very good meeting" on Saturday with Iranian foreign minister Mohammad Javad Zarif, who had Muslim services on Friday.
French foreign minister Laurent Fabius was also cautiously optimistic, telling reporters: "I hope that we are finally entering the last phase of this negotiation."
The diplomats spoke ahead of Monday's target date for a pact meant to impose long-term, verifiable limits on nuclear programmes that Tehran could modify to produce weapons. Iran, in return, would get tens of billions of dollars in sanctions relief.
The nuclear talks are now in their 16th day and have been extended three times since the first deadline of March 31 of the current round was missed. The mood among negotiators has turned more sombre each time a new target date was set.
As the weekend approached, Kerry declared the talks could not go on indefinitely and warned that the US could walk away from the negotiations.
But in another sign that a deal could soon be sealed, Russian news agencies reported that Russian foreign minister Sergey Lavrov planned to arrive in Vienna on Sunday evening. Most other foreign ministers of the six nations negotiating with Iran are already in the Austrian Capital and in position to join Kerry and Zarif for any announcement of an agreement.
Diplomats familiar with the talks say most of the nuts and bolts of implementing the deal have been agreed upon. But over the past week, issues that were previously on the back burner have led to new disputes. Among them is Iran's demand for a lifting of a UN arms embargo and its insistence that any UN Security Council resolution approving the deal be written in a way that stops describing its nuclear activities as illegal.
A diplomat said disagreements also persist on how long some of the restrictions on imports of nuclear technology and other embargos outlined in any new Security Council resolution will last. The diplomat, who demanded anonymity as confidential talks are not allowed to be discussed, said restrictions will last for years, not months.
Despite Kerry's relatively upbeat take, comments by Iran's supreme leader suggested that Tehran's mistrust of Washington would persist no matter what the outcome of the talks.
Iran's state-run Press TV cited Ayatollah Ali Khamenei on Saturday as calling the US an "excellent example of arrogance". It said Khamenei told university students in Tehran to be "prepared to continue the struggle against arrogant powers".
Even if Khamenei isn't signaling that the talks have failed, his comments appeared to be a blow to US hopes that an agreement will lead to improved bilateral relations that could translate into increased cooperation for a common cause -- the fight against Islamic State radicals.
Zarif had hinted at the same last week, suggesting a deal acceptable to his country will open the door to joint efforts on that front.
Israeli Prime Minister Benjamin Netanyahu, a fierce opponent of what he considers a deal that is too lenient on Tehran, said Khamenei's comments showed that Western powers are "caving" into Iran even as the Islamic Republic keeps railing against them.