The International Atomic Energy Agency, the UN watchdog overseeing Iran’s geopolitically incendiary nuclear programme, might turn out to have bite as well as bark.

Its latest report, under the leadership of Japanese diplomat Yukiya Amano, who in December replaced Mohamed ElBaradei, the IAEA’s long-serving Egyptian chief, comes close to accusing Tehran of running a covert atomic weapons programme.

Leading western powers might have long suspected that; Iran’s Arab neighbours might fear it; and Israel might hold it as an article of faith. But until now the IAEA has been reticent to come out as forthrightly as this without clear proof. The marked shift in tone comes as the US and Europe try to push a new round of sanctions against Iran through the Security Council, and as Israeli officials make clear that they will not stand by and watch Iran go nuclear – and, almost openly, discuss when, rather than whether, to bomb its nuclear facilities.

Incendiary indeed – and made more so by Iranian policy becoming so erratic that it is not just hard to know how to formulate a response but to know who to send it to.

One extraordinary development was buried in paragraph 12 of the IAEA report. Iran, on February 14 and in the presence of the agency’s inspectors, moved about 1,950kg of low-enriched uranium (LEU) from the fuel enrichment plant at Natanz to a pilot plant there. In other words, it moved almost its entire stock of LEU from a functioning enrichment facility 22 metres underground and encased in 2.5 metres of concrete to an unprotected skeleton facility on the surface.