The signatories to the faltering Iran nuclear deal meet in Vienna on Tuesday as the US is urging international sanctions on the Islamic republic to be reimposed and an arms embargo to be extended.
Britain, France, Germany, China and Russia are struggling to save the 2015 landmark accord with Iran, which has been progressively stepping up its nuclear activities since last year.
Tehran insists it is entitled to do so under the deal – which swapped sanctions relief for Iran's agreement to scale back its nuclear programme – following the US withdrawal from the accord in 2018 and the reimposition of sanctions.
In a boost to Tuesday's talks, the Iranian atomic energy last week agreed to allow inspectors of the UN nuclear watchdog to visit two sites that allegedly hosted undeclared activity in the early 2000s.
The International Atomic Energy Agency head Rafael Grossi had travelled to Iran on his first trip since taking up the top post last year and after months of calling for access.
Results from any site visits are, however, expected to take three months, according to a diplomat familiar with the matter, so "it risks being a problem then with the Iranians" if anything undeclared and nuclear-related is found.
Mikhail Ulyanov, Russia's Ambassador to International Organisations in Vienna, said on Twitter on Monday that "nuclear deal participants have a lot of topics to discuss".
The meeting will be chaired by EU senior official Helga-Maria Schmid with deputy foreign ministers or political directors from Britain, China, France, Germany, Iran and Russia attending.
Mark Fitzpatrick, an associate fellow of the International Institute for Strategic Studies (IISS), said last week's agreement on access kept "Iran generally in line with the rest of the world, against an isolated United States".
The United Nations last week blocked the US bid to reimpose international sanctions on Iran, while Washington also failed to rally enough support to extend an arms embargo set to lapse in October.
But Mr Fitzpatrick pointed out that "Iran's nuclear activities remain of deep concern to those states that are dedicated to non-proliferation".
Iran reportedly recently transferred advanced centrifuges used to enrich uranium from a pilot facility into a new hall at its main Natanz nuclear fuel plant, which was hit by sabotage in July.
An IAEA assessment published in June said Iran's stockpile of enriched uranium was almost eight times the limit fixed in the accord.
The level of enrichment is still far below what would be needed for a nuclear weapon, but EU parties to the deal have urged Iran's full compliance.
The IAEA, which regularly updates its members on Iran's nuclear activities, is expected to issue a new report ahead of a meeting of member states to discuss the dossier later this month.