The European Union says there is "an advancement" in a long-anticipated trade mechanism, called the INSTEX, with Iran, after Tehran's announcement of further cuts in its commitments under a 2015 nuclear accord it signed with major world powers.

"There is an advancement when it comes to this instrument and the first transactions are being processed. It does take time but it is moving ahead so that process continues," the spokeswoman for EU foreign policy chief Federica Mogherini, Maja Kocijancic, told reporters in Brussels on Friday.

Iran on Thursday informed the European Union that it will begin unlimited nuclear research and development work from Friday, officially unleashing the third stage of its measured responses to Europe's lack of action in the face of Washington's violation of the nuclear deal, officially known as the Joint Comprehensive Plan of Action (JCPOA).

Iranian Foreign Minister Mohammad Javad Zarif told the EU foreign policy chief in a letter that Iran was further scaling back its commitments under the JCPOA due to the inability of the deal's three European signatories -- Britain, France and Germany -- to meet their end of the bargain.

Zarif's letter came after Iranian President Hassan Rouhani said on Wednesday that the country will expand its nuclear research and development as of September 6, setting aside the restrictions imposed on the country's research and development (R&D) in the JCPOA.

"We took the first step in reducing our commitments, and gave the P4+1 a two-month deadline. Then we went ahead with the second phase, giving them another two-month deadline. In the four-month period, we held negotiations with the P4+1, including the European Union and the three European countries in particular," Rouhani said.

Iran has rowed back on its nuclear commitments twice in compliance with articles 26 and 36 of the JCPOA.

Tehran says its reciprocal measures will be reversible as soon as Europe finds practical ways to shield the Iranian economy from unilateral US sanctions which were imposed last year when President Donald Trump withdrew from the nuclear deal.

European signatories to the JCPOA have so far failed to uphold their commitments. They have expressed vocal support for the deal, but failed to provide meaningful economic incentives as required under the nuclear agreement.

The three European signatories to the JCPOA unveiled late in January the long-awaited direct non-dollar payment mechanism meant to safeguard their trade ties with Tehran following the US withdrawal and in the face of Washington's "toughest ever" sanctions against the Islamic Republic. The INSTEX aims to barter humanitarian and food goods with Iran without using the US Dollar currency.

Elsewhere in her Friday media briefing, Kocijancic emphasized the European Commission's reliance on the International Atomic Energy Agency (IAEA) being able to monitor Iran's activities.

The United Nations nuclear agency has a "key role... in monitoring and verifying the implementation by Iran of the nuclear commitments" under the JCPOA, she said.

"Our commitment to the nuclear deal depends on full compliance by Iran," she said, noting that the EU based its assessment of that "on the reports done by the International Atomic Energy Agency."

Kocijancic pointed to the Iranian foreign minister's letter to the EU foreign policy chief and expressed "great concern" at Tehran's shrinking back from the 2015 nuclear deal.

She called on Iran to "reverse all activities that are inconsistent with its commitments... and to refrain from any further measures that undermine the preservation and full implementation of the nuclear deal."

Speaking to reporters after his press briefing in the Bangladeshi capital, Dhaka, on Wednesday, the Iranian foreign minister hailed France’s diplomatic efforts to save the multilateral nuclear deal, stressing, however, that Tehran is expecting practical steps by the Europeans aimed at guaranteeing Iran’s oil revenues.

“… what is determining for us are the developments on the ground, that is the measures that the Europeans need to take in paying or purchasing Iran’s oil,” Zarif said.

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