"It is crucial that the IAEA be able to resume its monitoring and verification activities as soon as possible so that the international community can receive assurances about the nature of Iran's nuclear programme," said the diplomat, asking not to be named.

"It is actions on the ground that will be decisive," they said, referring to a decision to reimpose sanctions on Iran.

"Iran must immediately implement measures requested by the IAEA."

Iran agreed a deal with the International Atomic Energy Agency (IAEA) on Tuesday, after it suspended cooperation following a 12-day war with Israel in June.

Israel and the US launched strikes in June on Iranian nuclear facilities, which the IAEA has not been able to access since.

Iran, which criticised the IAEA for failing to condemn those strikes, has said future cooperation with the agency would take "a new form".

In an interview aired Wednesday Iranian Foreign Minister Abbas Araghchi said Iran was withholding access to UN nuclear inspectors despite the deal. The agreement itself does not create any access, he added.

Western countries accuse Iran of seeking to acquire nuclear weapons -- something Tehran denies, defending its right to what it insists is a civilian nuclear program.

In late August, France, Germany and the UK triggered a mechanism to reimpose UN sanctions on Iran for failing to comply with commitments over its nuclear programme signed a decade ago.

They gave Iran a month to negotiate before sanctions were reimposed.