US Secretary of State Antony Blinken said Thursday it was not too late for Iran to revive its nuclear deal with world powers, but cautioned that optimism was low.
"I have to tell you, recent moves, recent rhetoric, don't give us a lot of cause for optimism," he said.
"But even though the hour is getting very late, it is not too late for Iran to reverse course" to save the 2015 deal aimed at preventing Tehran from building an atomic bomb, Blinken told reporters in Stockholm on the sidelines of a meeting of the Organisation for Security and Cooperation in Europe (OSCE).
In a phone call with Blinken on Thursday, Israeli Prime Minister Naftali Bennett called for the "immediate cessation" of talks between Iran and major powers in Vienna, which resumed on Monday after a five-month hiatus.
Blinken declined to comment directly on the request.
"We're going to know very, very quickly, I think in the next day or two, whether Iran is serious or not," he said.
"In the very near future, the next day or so, we will be in a position to judge whether Iran actually intends now to engage in good faith."
The 2015 agreement offered Iran a lifting of economic sanctions in return for strict curbs on its nuclear activities.
The goal was to make it practically impossible for Iran to build an atomic bomb, while allowing it to pursue a civilian nuclear programme.
But the deal started to unravel in 2018 when then US president Donald Trump pulled out and began imposing sanctions on the Islamic republic.
In turn, Iran, which denies it wants to acquire a nuclear arsenal, has gradually abandoned its commitments since 2019.
US President Joe Biden has said he is willing to return to the deal as long as Iran also resumes the original terms.