Earlier this week, European powers and the United States formally submitted a censure motion critical of Iran to the board of governors of the International Atomic Energy Agency (IAEA).

Western powers have repeatedly expressed concern over Tehran's decreased cooperation with the agency, as tensions have run high ever since a 2015 deal curbing Iran's nuclear programme in exchange for sanctions relief fell apart.

The censure motion brought by Britain, France, Germany and the United States says it is "essential and urgent" for Iran to "act to fulfil its legal obligations".

The confidential resolution seen by AFP also calls on Tehran to provide "technically credible explanations" for the presence of uranium particles found at two undeclared locations in Iran.

Furthermore, Western powers are asking for a "comprehensive report" to be issued by the IAEA on Iran's nuclear efforts "at the latest" by spring 2025.

The resolution is expected to come to a vote on Thursday evening, diplomats told AFP.

- Differences laid bare -

Since 2021, Tehran has significantly decreased its cooperation with the agency by deactivating surveillance devices to monitor the nuclear programme and barring UN inspectors.

At the same time, Iran has rapidly ramped up its nuclear activities, including increased stockpiles of enriched uranium, which has heightened fears that Tehran might be seeking to develop a nuclear weapon.

Iran denies wanting to develop a nuclear weapon.

The resolution comes just as IAEA head Rafael Grossi returned from a trip to Tehran last week, where he appeared to have made headway.

During the visit, Iran agreed to an IAEA demand to cap its sensitive stock of near weapons-grade uranium enriched up to 60 percent purity.

"This is a concrete step in the right direction," Grossi told reporters Wednesday, saying it was "the first time" Iran had made such a commitment since it started breaking away from its obligations under the 2015 deal.

The landmark 2015 deal fell apart three years later after the unilateral withdrawal by the United States under then-president Donald Trump.

In retaliation, Tehran began rolling back some of its commitments by increasing its uranium stockpiles and enriching beyond 3.67 percent purity -- enough for nuclear power stations -- permitted under the deal.

- Potential to 'harm efforts' -

Ahead of the vote, Iran's Foreign Minister Abbas Araghchi sounded another warning on Thursday, saying that adopting the censure "will weaken and disrupt" interactions between the agency and Tehran.

Araghchi had warned earlier of a "proportionate and appropriate" response by Iran if the board passes the resolution.

According to Heloise Fayet, a researcher at the French Institute of International Relations, the resolution has the potential to "harm Rafael Grossi's efforts".

"But Western powers are frustrated by the lack of effectiveness of his diplomatic manoeuvres and are looking for firmer solutions," she told AFP.

On Wednesday, Grossi said he could "not exclude" that Iran's commitment to cap enrichment might falter "as a result of further developments".

Foreign policy expert Rahman Ghahremanpour said Tehran might retaliate to the new censure by "increasing the enrichment levels".

But he does not expect any drastic "strategic measures" as Iran does not want to "aggravate tensions" before Donald Trump returns to the White House.