Yukiya Amano, director-general of the International Atomic Energy Agency (IAEA) reiterated in a statement that "Iran is subject to the world's most robust nuclear verification regime" and that the 2015 Joint Comprehensive Plan of Action (JCPOA) was "a significant verification gain".

"The IAEA is closely following developments" related to the JCPOA, Amano said.

He previously said the JCPOA's loss would be "a great loss for nuclear verification and for multilateralism".

The other parties are now looking into ways to salvage the agreement, with the foreign ministers of France, Britain and Germany due to meet Iranian representatives next Monday.

Despite US criticism that the accord does not go far enough in monitoring Iran's nuclear activities, the IAEA points to the fact that its inspectors now spend 3,000 man days per year on the ground in Iran.

The agency says it has attached some 2,000 tamper-proof seals to nuclear material and equipment, and that it has access to "hundreds of thousands of images captured daily by our sophisticated surveillance cameras", the number of which has almost doubled since 2013.