Analysts say preparations would be visible, and they are 'quite certain' there are no hidden facilities; likely Moscow would want West to see what it is doing as a warning

Military says Putin to monitor the large-scale exercise on Saturday, as tensions with West at highest level since Cold War

The president has the sole authority to order a US nuclear attack, but some safeguards do exist

Tehran also accused of proliferating ballistic missile technology in the region; Iran insists all its missile activities are legal and not nuclear-related