The Joint Commission of the 2015 nuclear deal convened at the level of political directors on Friday in Vienna, Austria, against a backdrop of mounting disputes over compliance with the agreement.

The session was jointly headed by Deputy Foreign Minister Abbas Araqchi and Secretary-General of the European External Action Service Helga Schmid.

Araqchi was set to hold bilateral meetings with his counterparts as well as the new head of the International Atomic Energy Agency, Rafael Grossi, on the sidelines of the event, ISNA reported.

The commission is a forum where the signatories can discuss problems regarding the implementation of the accord, formally known as the Joint Comprehensive Plan of Actions.

The United States pulled out of the deal last year and reimposed sweeping sanctions on Tehran, forcing it to gradually scale back its commitments in response after the remaining parties proved unable to offset the effects of US pressure.

Iran has so far exceeded limits on nuclear enrichment purity and stockpiles of enriched uranium, as well as research and development, including the deployment of advanced centrifuges used to enrich uranium.

In the most recent phase of its plan in early November, Iran began uranium enrichment at the Fordow nuclear facility where the activity was banned under JCPOA until 2030.

The European parties, which have seriously fallen short of fulfilling their pledges to protect Iran's interests, kept calling on Iran to return to compliance, but the latest move drew their strong reaction.

France, Germany and Britain issued a joint statement immediately, warning of triggering JCPOA's dispute resolution mechanism that could culminate in the United Nations Security Council with a so-called snapback of global sanctions on Tehran.

Iranian officials argue that its nuclear steps are based on the provisions of JCPOA when a party is deemed to be out of compliance.

They also maintain that the measures are aimed at inducing the remaining parties to take effective action to uphold Iran's rights and will be immediately reversed once the country's economic issues are addressed.

German Foreign Ministry Spokesman Christofer Burger told reporters in Berlin, however, that the approach was "unacceptable" and that diplomats would make that clear at the Vienna meeting.

"We will underscore that Iran must fully reverse its breaches of the JCPOA," he said, AP reported.