Police stand outside a hotel where a meeting of the Joint Commission of the Joint Comprehensive Plan of Action (JCPOA), or Iran nuclear deal, is held in Vienna, Austria, April 20, 2021

The lack of an interim agreement between the UN nuclear watchdog and Iran on the monitoring of atomic activities is a serious concern that has been communicated to Tehran, US Secretary of State Antony Blinken said on Friday.

Struck on Feb. 21, the interim monitoring deal was valid for three months, then extended by a month on May 24. The International Atomic Energy Agency has said it expired on Thursday. It is in talks with Iran on another extension.

“This remains a serious concern,” Blinken told reporters at a news conference in Paris alongside his French counterpart Jean-Yves Le Drian. “The concern has been communicated to Iran and needs to be resolved.

A spokesman for the IAEA said that Director General Rafael Mariano Grossi would inform the IAEA Board of Governors on the matter during the course of Friday.

Iran struck a deal with major powers in 2015 to curb its uranium enrichment program, a possible pathway to nuclear arms, in return for the lifting of US., European Union and UN sanctions.

Former US President Donald Trump abandoned the deal in 2018 and reimposed harsh sanctions, prompting Tehran to start violating some of the nuclear limits in 2019 while sticking to its position that it had no nuclear weapons ambitions. US President Joe Biden is seeking to revive the agreement.

All sides have been negotiating in Vienna for six weeks to find a way to resume compliance, but a sixth round of indirect talks adjourned on Sunday with key issues still unresolved

“We still have significant differences with Iran,” Blinken said, adding that he hoped a resumption of talks in the coming days could resolve them.

Blinken, who said talks would not last indefinitely, said the immediate priority was to put the nuclear deal “back in the box,” but that the United States and its partners would also have the tools if a deal was agreed to handle Iran’s regional and missile activities.

Le Drian echoed those comments saying the ball was in the court of Iran’s decision makers and that the negotiations had now entered their toughest stage.

“We’re waiting for Iranian authorities to take the final difficult decisions to allow for the revival of the 2015 nuclear deal,” he said.