Iran this week disconnected some cameras allowing international inspectors to monitor its nuclear activities in response to a Western resolution passed June 8 in which the UN agency denounced Tehran's lack of cooperation.

Twenty-seven surveillance cameras "have been removed," IAEA Director General Rafael Grossi said in an interview broadcast Sunday by CNN, calling it a "very serious move."

"Recent history tells us that it is never a good thing to start saying to international inspectors, go home... things get much more problematic," he added.

The 2015 deal, known as the Joint Comprehensive Plan of Action, gave Iran relief from crippling economic sanctions in exchange for curbs on its nuclear activities.

But in 2018, then-US president Donald Trump unilaterally pulled out of the pact and reimposed sanctions, prompting Iran to begin rolling back on its own commitments.

Talks to revive the deal have stalled since March.

In the CNN interview, Grossi said he was telling his Iranian counterparts, "We have to sit down now, we have to redress the situation, we have to continue working together.

"The only way for Iran to get the confidence, the trust they so badly need in order to move their economy forward... is to allow the inspectors of the IAEA to be present."

Without the surveillance cameras, Grossi said, his agency will soon be unable to declare whether the Iranian nuclear program is "peaceful" -- as Tehran has repeatedly insisted -- or whether Iran is developing an atomic bomb.

Even if the Iranians reconnect the cameras in a few months, Grossi said, whatever work they do in the meantime will remain secret, possibly rendering useless any agreement.

Therefore, he said, the recent Iranian action makes "the way back to an agreement extremely more difficult."

While Trump pulled the United States out of what he said was a badly flawed accord, his successor Joe Biden has said he is ready to again embrace the deal so long as Iran also respects its own commitments.

But negotiators have met with repeated frustration, and the possibility of failure appears closer than ever.

In a call Saturday with Iranian Foreign Minister Hossein Amir-Abdollahian, UN Secretary-General Antonio Guterres called on diplomats to rescue the agreement, according to a Sunday statement.