U.S. intelligence agencies had long assessed that, faced with the possibility of an attack on its nuclear facilities, Iran would try to move its stockpile.

The nuclear watchdog chief Rafael Mariano Grossi told Fox News there was "no information" about the material's whereabouts.

The recent US and Israeli airstrikes on Iran’s key nuclear facilities have inflicted significant damage but left major uncertainties about the status of Iran’s nuclear programme—most notably, the fate of 400 kg of enriched uranium.