Iran and global nuclear watchdog, the IAEA struck a temporary deal to allowing inspection.
It would enable the agency to retain the “necessary degree of monitoring and verification work”, IAEA chief Rafael Grossi said, without going into detail.
Under the plan, for the next three months Iran would hold recordings from monitoring equipment installed at sites by the IAEA but would not release the information unless sanctions were lifted within that timeframe, the Atomic Energy Organisation of Iran (AEOI) said. If sanctions remained, the data would be erased, it added.
Cameras and other apparatus have been put in place by the IAEA to help verify that Iran does not carry out nuclear activities prohibited under the deal.
It comes ahead of a deadline set by Iran to stop intrusive checks of sites unless US sanctions are lifted.
Tensions have soared since the US left a nuclear deal with Iran in 2018.
Former President Donald Trump re-imposed crippling economic sanctions to force Iran to renegotiate the accord. Iran refused and retaliated by rolling back a number of key commitments.
The crisis over Iran’s nuclear programme has been on the international agenda for almost 20 years. Iran says the programme is for peaceful purposes, while the US and others suspect Iran has ambitions to develop nuclear weapons.