The US, Britain, France and Germany on Monday urged Iran to "immediately reverse" its decision to withdraw accreditation from top UN nuclear inspectors.
The "disproportionate and unprecedented" move to bar International Atomic Energy Agency (IAEA) inspectors would seriously hamper the watchdog's work in Iran, the organisation said on Saturday.
The decision concerned eight inspectors, all from France and Germany, Iranian state media reported.
"Iran must immediately reverse these inspector de-designations and fully co-operate with the agency to enable them to provide assurances that Iran's nuclear programme is exclusively peaceful," the permanent representatives of the four countries to the IAEA said in a statement.
The four "will continue to stand in strong support of the IAEA and the international safeguards verification regime on which the world's security relies", they said.
IAEA Director General Rafael Grossi on Monday also urged Iran to reconsider its decision, warning that its failure to co-operate would carry severe consequences.
"If they do not co-operate with the IAEA, they will not get what they want: the assurances they want to see, the confirmation they want to see, the approval of the international community," Mr Grossi told AFP.
Iran's nuclear programme - in pictures
Brussels, which acts as co-ordinator for the 2015 nuclear deal between Tehran and world powers, on Sunday said it was "highly concerned" by the development.
In 2015, major world powers reached the accord with Iran under which Tehran would curb its nuclear programme in exchange for relief from crippling economic sanctions.
But that started to unravel in 2018 when then-US president Donald Trump withdrew from the deal and reimposed sanctions.
Tehran increased its nuclear programme, while continuing to deny that it harbours ambitions of developing nuclear weapons capability.
Efforts to revive the deal have been fruitless so far.
