US Secretary of State Antony Blinken reiterated on Thursday that “the ball remains” in Iran’s court regarding an agreement to revive the 2015 nuclear deal, JCPOA.

Speaking to reporters in Pittsburgh, Pennsylvania, Blinken repeated that time is running out for resuming productive negotiations, as Iran builds up its stockpile of enriched uranium.

“Because of the work that Iran is doing on its nuclear program in violation of the JCPOA – spinning more sophisticated centrifuges, building up stockpiles of uranium enriched to 20 percent or even 60 percent – 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,” Blinken said.

Iran began violating enrichment levels in 2019, set by the JCPOA, as retaliation against sanctions imposed by the former US administration that withdrew from the agreement in 2018.

President Joe Biden announced his intention to return to the nuclear agreement during last year’s presidential campaign, which would entail lifting tough sanction the Trump administration had imposed.

In April, talks began in Vienna between Iran and world powers who have remained in the agreement. The US participated in the talks indirectly, as Tehran refused to negotiate directly with Washington. But the talks were suspended in June after a new president was chosen in Iran. So far, more than a month after the formation of a government, Iran has still not returned to the talks, saying that it is studying the issue.

In response to a question about reports that Washington has appealed to Beijing to reduce its oil purchases from Iran to pressure it to return to the talks, Blinken spoke generally of the role other world powers need to play in to “prevail upon Iran to quickly return and see if we can still get back to the JCPOA.”

“So, there is a limited runway on that and the runway is getting shorter,” Blinken said.