Iran steps up nuclear threat from bunker underneath a mountain
Iranian experts have carried out the necessary preparations at Fordow near the holy city of Qom.
It paves the way for the Islamic state to begin higher-grade uranium enrichment at the site on a former military base.
The machines, equipment and nuclear material needed have been transferred and installed at Fordow, the sources added.
They suggested the work itself - until now conducted above ground at another location - could start when Iran takes the decision.
It coincides with a period of escalating tension between Western powers and President Mahmoud Ahmadinejad after a U.N. nuclear watchdog report last month said Tehran appeared to have worked on designing a nuclear weapon, and that secret research may continue.The United States and its European allies have seized on the unprecedented document by the U.N. International Atomic Energy Agency to ratchet up the sanctions pressure on Iran, one of the world's largest oil producers. Read More