The UN nuclear watchdog said there had been “no progress” in talks with Tehran on disputes over the monitoring of Iran"s atomic programme, just days before talks restart on reviving the 2015 Iran nuclear deal.

Rafael Grossi, director general of the International Atomic Energy Agency (IAEA), told a quarterly meeting of the agency’s board that talks he held in Tehran on Tuesday were “inconclusive” despite being “constructive”.

Grossi had sought to tackle constraints put on IAEA inspections earlier this year, outstanding questions over the presence of undeclared nuclear material at sites in Iran, and the treatment of IAEA staff in the country.

“In terms of the substance... we were not able to make progress”, - Grossi told reporters, saying that the lack of agreement had come “in spite of my best efforts”.

Behrouz Kamalvandi, spokesman for the Atomic Energy Organization of Iran, told Iranian television his team “tried until the last moment” but there is still work to be done.

Among other officials in Tehran, Grossi met Foreign Minister Hossein Amir-Abdollahian.

Amir-Abdollahian put a positive gloss on the talks, telling the official Irna agency on Wednesday that a “common declaration” had been reached which would be published “as soon as possible”.