Being near a finishing line was different to crossing it, Iran’s chief negotiator in the Vienna nuclear talks tweeted Thursday.

Reaching agreement over reviving the 2015 Iran nuclear deal, Ali Bagheri Kani wrote, “requires extra caution, much perseverance, additional creativity and balanced approach to take the last step… To finish the job, there are certain decisions that our western interlocutors need to take.”

Talks in Vienna have faced the challenge of identifying which United States sanctions contravene the 2015 agreement, which the US left in 2018, and exactly how Iran’s nuclear program, expanded since 2019, would be brought back within the limits of the agreement, the JCPOA (Joint Comprehensive Plan of Action).

Bagheri-Kani returned to Tehran Wednesday night for consultations, leaving colleagues to continue discussions. Iran’s foreign ministry announced his return to Tehran should not be seen as a sign of imminent agreement in Vienna.

Iranian Foreign Minister Hossein Amir-Abdollahian spoke by phone Thursday with his British counterpart Liz Truss, saying that restoring the JCPOA needed “a serious will to make a courageous and realistic political decision” that recognised Iran's interests and secured stability. Tehran has sought guarantees that the US would not again leave the JCPOA.

Amir-Abdollahian told Truss that the United Kingdom needed to pay a £400-million (around $540-million) debt owed Iran since 1971.