"This will be communicated to the ambassadors of the five countries" still party to the deal -- Britain, China, France, Germany and Russia -- at a meeting on Wednesday with Iranian Deputy Foreign Minister Seyed Abbas Araghchi, IRNA reported.

A foreign diplomat in Tehran confirmed to AFP that the ambassadors of the five countries had been invited to a meeting with Araghchi on Wednesday at the foreign ministry.

The US unilaterally withdrew on May 8, 2018 from the 2015 multilateral deal known as the Joint Comprehensive Plan of Action (JCPOA) under which Iran agreed to halt its nuclear programme in exchange for the lifting of biting sanctions.

President Hassan Rouhani is also set to send a letter to the five countries' heads of state in order to "clearly emphasise how much Iran has commanded patience regarding the JCPOA," IRNA reported.

"But opportunities have been lost, and the counterparts have been unable to live up to their commitments in the JCPOA, in a way that Iran is left no way but to reduce its commitments," the news agency said, adding that Rouhani's letter would be a "political" one.

Foreign Minister Mohammad Javad Zarif was also expected to explain the "technical and legal details of reduction of Iran's commitments" in a separate letter to Federica Mogherini, the European Union's foreign affairs chief.

According to IRNA, Iran would reduce its commitments in two phases, with the second coming two months after the first.

"If the counterparts do undertake any new measures Iran will return to the previous situation" before it cut its commitments, it reported, without elaborating on which commitments Iran would step back from.

"Iran's clear request is for the banking and oil situation to return to before the US withdrawal" in May 2018, IRNA said.

The three European parties to the deal -- Britain, France and Germany -- tried to save the accord with a trade mechanism meant to bypass reimposed US sanctions, but their attempt was dismissed by Iran's supreme leader Ayatollah Ali Khamenei as a "bitter joke".