The missile shield, which the US sees as vital to defend itself and Europe from rogue states, costs 800 million dollars. Tomorrow the US will begin the construction on a final site in northern Poland that should be ready by the end of 2018. The shield was first proposed almost a decade ago and it also includes ships and radar installations across Europe. It will be handed over to NATO in July, with command and control run from a U.S. air base in Germany.

“As long as Iran continues to develop and deploy ballistic missiles, the United States will work with its allies to defend NATO” said U.S. Deputy Defense Secretary Robert Work, at the remote Deveselu air base, which was declared operational.

However, Russia says the shield is aimed at blunting its own nuclear arsenal. Kremlin is highly dissatisfied by the show of force by its Cold War rival in formerly communist-ruled Eastern Europe.

“It is part of the military and political containment of Russia” Andrey Kelin, a senior Russian Foreign Ministry official said on Thursday. “These decisions by NATO can only exacerbate an already difficult situation” he added, saying the move would hinder efforts to repair ties between Russia and the alliance.

The activation and the expansion of the shield also comes as NATO prepares a new deterrent in Poland and the Baltics, following Russia's 2014 annexation of Crimea. In response, Russia is reinforcing its western and southern flanks with three new divisions.

Also, Russia has stationed anti-aircraft and anti-ship missiles in Kaliningrad, located between Poland and Lithuania, able to cover huge areas and complicate NATO's ability to move around. Poland now fears that Russia may retaliate further by announcing the deployment of nuclear weapons there.

“Missile defense … does not undermine or weaken Russia's strategic nuclear deterrent” NATO Secretary General Jens Stoltenberg said at the Deveselu base. But, both US and NATO officials remained vague on whether the radars and interceptors of the umbrella could be reconfigured to defend against Russia in a conflict.