VIENNA: The head of the UN nuclear watchdog said Wednesday that it would “never abandon” its attempts to get Iran to clarify the previous presence of nuclear material at several undeclared sites there. Iran has said the closure of the probe is necessary in order to clinch a deal to revive the 2015 deal with world powers on its nuclear programme.

However, on Wednesday International Atomic Energy Agency (IAEA) Director General Rafael Grossi insisted that it would “never abandon a process... because of a political reason”.

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“This is not how the IAEA works,” he told reporters at a press conference. The IAEA has been pressing Tehran for several years for explanations regarding indications that nuclear material was previously present at four different locations in Iran.

While much of the activity concerned is thought to date back to the early 2000s, sources say that one of the sites, in the Turquzabad district of Tehran, may have been used for storing uranium as late as the end of 2018. Iranian Foreign Ministry spokesman Saeed Khatibzadeh said on Monday that unless this issue is closed, “we can’t think of the possibility of an agreement about the return of the US” to the Iran nuclear deal.