Former Iranian President Hassan Rouhani has said the revival of the nuclear deal was possible a year ago, noting that the situation has become more complicated.

Speaking to a group of his former officials on Sunday, Rouhani stressed the need for lifting economic sanctions, which is tied to restoring the 2015 nuclear agreement, officially known as the Joint Comprehensive Plan of Action (JCPOA).

He added that the administration of Ebrahim Raisi should not miss the opportunity to reach an agreement with world powers.

Talks began more than a year ago -- when Rouhani was still in office -- in Vienna to revive the JCPOA, and the negotiating sides had reportedly reached some initial agreements until Iran’s presidential elections in June when Tehran stopped the talks for five months. According to reports, about “70 to 80 percent" of the draft agreement was prepared during Rouhani’s term.

The negotiations continued under Raisi, but they seem to have reached a dead-end as they have stalled since mid-March, primarily because of Tehran’s demand to remove its Revolutionary Guard (IRGC) from a US list of terrorist organizations.

The Biden administration so far has not accepted Iran’s demand for delisting the IRGC, as more domestic pressure has emerged in Washington against such a move. Almost all Republicans and many Democrats oppose concessions to Iran.

Enrique Mora, the European Union coordinator for the talks, is scheduled to visit Tehran on Tuesday to exchange views of Tehran and Washington, in what seems to be among the last measures to resolve the remaining issues.