Nuclear talks between world powers and Tehran hit a new snag after Iran apparently again turned down US demands for concessions, leaving negotiations in limbo just three days before a deadline for a deal.
In hours of high drama reflecting the delicate stage of the talks, both US secretary of state John Kerry and Iranian foreign minister Mohammad Javad Zarif first made, then cancelled plans to walk away from the talks - at least temporarily - for additional consultations.
Such developments could have meant possible progress, suggesting that the Iranians needed political approval from Tehran to move forward.
After initially announcing he was flying to Paris, Mr Kerry suddenly reversed course and scheduled a new meeting with Mr Zarif, with the two talking into the evening for more than two hours.
Iranian media initially spoke of a new US initiative that Mr Zarif needed to have his superiors sign off, but the Iranian diplomat dashed those hopes.
"There have been a lot of discussions in Vienna, but there were no remarkable offers and ideas to take to Tehran," Mr Zarif told Iran's official IRNA news agency.
The remark reflected the probability that substantial obstacles remain in the way of a deal that would cap Iran's nuclear programme in exchange for sanctions relief - a view reinforced by senior diplomats of other nations taking part in the negotiations.
The Russian Foreign Ministry said that a phone call between Mr Kerry and Russian foreign minister Sergey Lavrov revealed that "more efforts are needed" to meet Monday's deadline for a deal. And after consulting in Vienna with participants in the talks, British foreign secretary Philip Hammond spoke of "a very significant gap between the parties".
Mr Kerry and Mr Zarif have both emphasised that there has been no discussion about extending the talks - for a second time - if the deadline is not met. At the same time, the stubborn differences increasingly suggest little choice than to agree to continue talking past Monday - or to call the negotiations a failure, something neither side can afford to do.
Breaking off the talks would embolden Iran to end a freeze on nuclear activities it says it needs for civilian purposes, but which can also be used to make atomic arms. Tehran could turn instead to expanding its atomic programme, reigniting the threat of Israeli and potential US military action.
Even if the deadline is missed, both sides hope they can persuade sceptics at home that enough progress was achieved to warrant further pursuit of a full deal.