The remarks came as French Foreign Minister Jean-Yves Le Drian, who is on an official visit to Tehran, threatened ahead of the visit that Iran needed to address global concerns over its ballistic missile program or it risked new sanctions.
The top French diplomat is scheduled to hold talks with his Iranian counterpart, Mohammad Javad Zarif, and President Hassan Rouhani during the day-long visit.
Iranian senior officials on Monday called for collective resolve by the European countries to protect the Iranian nuclear deal reached in 2015.
France has ballistic missiles with ranges of more than 6,000 kilometres, which can be launched from submarines, but Le Drian said Iran was risking fresh sanctions if it did not curb its missile programme, which is now limited to 2,000 kilometres.
Le Drian arrived in Tehran on Monday for talks with Iranian officials on mutual ties as well as regional and global issues.
On May 12, Donald Trump is expected to decide whether to continue waiving sanctions under a USA law.
Iran honors its commitment to the treaty to limit its nuclear development plan as the International Atomic Energy Agency has certified on nine occasions.
But the key focus has been the 120-day deadline set by Trump in January for USA lawmakers and European allies to "fix" the nuclear deal, removing "sunset clauses" that mean it expires in 2026 and reining in Iran's missile programme and regional activities.
As mentioned by the confidential IAEA report, Amano also said the agency had requested clarification from Iran about its plans for nuclear-powered naval vessels, suggesting the IAEA has still not heard back from the Islamic Republic.
Yukiya Amano said that if the deal "were to fail it would be a great loss for nuclear verification and multilateralism".
Iran has stayed within the deal's restrictions since Trump took office but has fired diplomatic warning shots at Washington in recent weeks.
Iran is not allowed to enrich uranium beyond 3.67 percent fissile purity under the deal, a level that is suitable for fuelling some civilian nuclear power stations and far short of the 80-90 percent that is considered weapons grade.
For his part, Le Drian hailed Iran's commitment to the JCPOA, saying that France insists on the full implementation of the deal.
French President Emmanuel Macron on Sunday voiced his support for the 2015 nuclear deal which limited Iran's nuclear activities in returns for the lift of western sanctions against Tehran.
"Any move to undermine the JCPOA would result in the loss of credibility of other worldwide agreements, " Shamkhani said.