Tehran may have used the delay in the US's potential strike to make the beneath-mountain facility nearly untouchable.

Iran is blocking the International Atomic Energy Agency (IAEA) from inspecting multiple sites of interest in its nuclear weapons development programme, a senior source in the European Union’s (E.U.’s) ...

Since the US bombed Iran's key nuclear sites last year, analysts say work has increased at a secret underground facility that could be used to restart Tehran's nuclear program.