On Wednesday the International Atomic Energy Agency (IAEA) and Iran reached an agreement on replacing cameras the TESA nuclear complex in Karaj, west of Tehran, after they were damaged in a June attack Iran blames on Israel.

However, in a press conference on Friday, IAEA Director General Rafael Grossi said no understanding had been reached with Iran over the issue of a missing data storage unit from one of the cameras.

Asked whether he thought it could have vanished in the June attack, Grossi replied: "We have doubts about that".

"This is why we are asking them 'Where is it?' I'm hopeful that they are going to come up with an answer because it is very strange that it disappears," Grossi said.

Wednesday's deal came as international diplomats continue negotiations over the possible revival of a 2015 nuclear deal between Iran and world powers, with Western countries warning time is running out for the talks.

In February Iran began restricting some IAEA inspection activity as part of steps away from the 2015 deal.

Those were in retaliation for the United States unilaterally pulling out of the deal in 2018 and reimposing crippling sanctions on Tehran.

Agreements have been reached between Iran and the IAEA to mitigate the impact of the restrictions but the agency has repeatedly warned that Tehran is threatening its ability to monitor its nuclear programme.

Grossi admitted there was "concern" about losing surveillance data at Karaj but added: "We have ways to try to reconcile the facts on the ground with what Iran is going to be telling us".

"Don't forget this is a facility we know very well, we know the kind of equipment there is," he said.

The IAEA's experts would use "analysis, projections, modelling" to try "to put the jigsaw puzzle together", he added.

For the rest of the cameras at Karaj, as well as at other sites where the IAEA's activity has been restricted since February, Iran has said the footage will only be available to the IAEA once US sanctions are lifted.

How and when Iran could get sanctions relief is one of the topics being discussed at the Vienna talks.

On Thursday, the head of the Atomic Energy Organization of Iran Mohammad Eslami said that Iran would inspect one of the cameras due to be installed at Karaj.

"An IAEA inspector will bring this new camera and explain its workings in the presence of our security and judiciary officials," Eslami said according to the Nournews agency.

Suspicions have been raised in Iran that June's attack could have been enabled by the hacking of the cameras.

Showing the reporters assembled at Friday's press conference an example of one of the cameras, Grossi dismissed as "absurd" the idea that they could have been involved in the June incident.