According to experts, the strategy of the world powers appears to be "pressuring Iran to bring the talks to a conclusion".
Several world powers have indicated that a deal – at least in principle – to revive the Iran nuclear accord may be just days away, but experts warn that failure still cannot be ruled out.
The outline of a new deal appears to be on the table in talks which have been held in Vienna since late November between signatories Britain, China, France, Germany, Russia – and the United States indirectly.
"The West, Russia, and China appear to be more aligned than at any prior point," said Henry Rome, analyst with the Eurasia Group.
The strategy of the world powers appears to be "pressuring Iran to bring the talks to a conclusion," the analyst said, adding that the negotiations appeared to nearing a "decision point".
A diplomatic source in Vienna confirmed this week that there had been "advances" in the talks.
The US State Department said on Thursday that "substantial progress" had been made, and that an agreement was possible within days if Iran "shows seriousness".
The day before French Foreign Minister Jean-Yves Le Drian had said a deal was "within grasp" but that "a serious crisis" was still possible if Iran refused to accept the proposals of the other parties.
Experts believe Iran is only a few weeks away from having enough fissile material to build a nuclear weapon – even if it would take several more complicated steps to create an actual bomb.
Iran has always denied it wanted to acquire atomic weapons, and on Thursday supreme leader Ali Khamenei called such claims "absurd".
Best and worst case scenarios
Iran's top negotiator Ali Bagheri called on the other parties to "avoid intransigence".
"We are closer than ever to an agreement; nothing is agreed until everything is agreed, though," he tweeted earlier this week.
Ali Vaez, Iran specialist at the International Crisis Group, said two scenarios are possible in the current conditions.
"If, in the next few days, the Iranians don't back off from some of their demands, then I think what you're likely to see is a Western walkout," he said.
That could lead to a resolution criticising Iran being put forward at the next Board of Governors meeting of the UN nuclear watchdog the International Atomic Energy Agency, due to begin on March 7.
Vaez said this could be the first step in a "cycle of escalation".
However, faced with multiple security crises in other parts of the world, Vaez said, "the last thing the Biden administration wants" is a nuclear proliferation headache in Iran.
The more optimistic scenario would entail "a breakthrough in ... the next four or five days" opening the door for a deal being "announced towards the end of this month or early March".