US Secretary of State Antony Blinken on Thursday renewed warnings that time was running out for Iran to return to the 2015 nuclear deal.
"The ball remains in their court, but not for long," Blinken was quoted by AFP as having told reporters in Pittsburgh where he took part in US-EU trade talks.
"There is a limited runway on that, and the runway is getting shorter," he added.
Blinken reiterated that President Joe Biden was willing to return the United States to the 2015 deal.
"Simply getting back to the terms of the JCPOA at some point will not be sufficient to recapture the benefits of the agreement because of the progress Iran has made," he added, using the acronym for the agreement.
The previous government, headed by former President Hassan Rouhani, had been holding indirect talks with the US on a return to the agreement.
The negotiations were adjourned on June 20, two days after Ebrahim Raisi won Iran's presidential election, and no date has been set for a resumption of dialogue.
A senior US official said last week that the window is still open to revive the 2015 Iran nuclear deal but won't be forever.
Blinken said on Thursday that the Biden administration has been engaged "in very good faith for many months" in the indirect talks in Vienna with Iran on returning to compliance.