Iran has done little to answer longstanding questions from the UN’s nuclear watchdog about the origin of uranium particles found at three undeclared sites despite a new push for a breakthrough, the watchdog said in a report seen by Reuters on Monday.

The lack of progress could trigger a new diplomatic row with the West when the International Atomic Energy Agency’s Board of Governors of 35 countries meet next week. If Western powers seek a resolution critical of Tehran, it could deal another blow to stalled efforts to revive the 2015 nuclear deal.

New IAEA quarterly report detailing Iran’s continued failure to provide satisfactory answers increases pressure on US and allies to take action against Iran at council meeting directors, since Tehran and the IAEA announced a new effort in March to clear things up now.

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“Iran has not provided technically credible explanations for the Agency’s findings on these sites,” the report said, adding, “Safeguards issues related to these three sites remain outstanding.”

A separate IAEA quarterly report seen by Reuters says Iran’s stockpile of 60% enriched uranium – nearly 90% or so weapons-grade, in a form that can be fed into uranium enrichment centrifuges – is said to have increased by 9.9 kg. at 43.1 kg.

This is more than what the IAEA calls a “significant quantity”, defined as “the approximate quantity of nuclear material for which the possibility of manufacturing a nuclear explosive device cannot be excluded” – or theoretically enough material, if it is further enriched, to make a nuclear bomb.

At 60% purity, a significant amount would be about 42 kg of uranium.

Western powers fear Iran is getting closer to being able to rush to produce a nuclear bomb if it chooses, although Iran says its intentions are entirely peaceful.

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