Global powers sought today to ramp up pressure on Iran as they struggled to strike a long-sought nuclear accord, with one Iranian official admitting "God only knows" if a deal was close.
With speculation rife about the fate of the tough negotiations, US Secretary of State John Kerry was to give an update on the situation to reporters at 1700 GMT, a US official said.
All bets remained off as negotiators held back-to-back meetings before tomorrow's effective deadline, hoping to end a 13-year standoff with Iran over its suspect nuclear programme.
If the US Congress does not receive the text by early tomorrow morning Vienna time -- midnight in Washington -- it will likely delay and complicate its implementation.
Two deadlines have already been missed during this round of negotiations alone which have now stretched into their 13th day.
Diplomats from various delegations ruled out a deal by the end of today, but when asked whether an accord would be possible Friday or Saturday, one Iranian official told AFP: "God only knows."
After almost two years of continuous negotiations, the so-called P5+1 group -- Britain, China, France, Germany, Russia and the United States -- wants to wrap up a deal to deny Iran the capability to make a nuclear bomb, in return for lifting biting international sanctions.
With the talks seemingly at deadlock, French Foreign Minister Laurent Fabius rejoined Kerry as well as his German and British counterparts early today, alongside Chinese and Russian officials, to plot a strategy forward.
Kerry then met briefly with Iranian Foreign Minister Mohammad Javad Zarif, and was due to hold another P5+1 meeting without Iran later in the day, before addressing the press.
All sides say huge progress has been made in the past days of negotiations -- the final stage of marathon talks first launched in September 2013.
Most of the final text is already written, along with most of five technical annexes.
Some of the thorniest issues such as a time frame for lifting sanctions, a UN probe into allegations that Iran in the past sought to develop nuclear weapons, also appear close to resolution.
