The US is to launch a new land-based Aegis ballistic missile defence system at Deveselu base in Romania.
The Aegis Ashore site in Deveselu, which is located around 100 miles west of Bucharest, is said to be critical for defending Nato's 28 members.
US Deputy Assistant Secretary of State for Defense Policy and Verification Operations Frank Rose said: "Combined with the missile-defence-capable ships in the Mediterranean, the site provides a significant enhancement to the coverage of Nato from short and medium-range ballistic missile threats originating from outside the Euro-Atlantic area."
Rose acted as the lead US negotiator for missile defence base agreements in Romania, Poland and Turkey.
The Nato command and control centre is located in Germany, while four US Aegis ballistic missile defence ships are homeported in Rota, Spain.
A groundbreaking ceremony for an Aegis Ashore site, due to become operational in 2018, is scheduled to be held in Redzikowo, Poland.
The Russian foreign ministry said that the activation of the European missile defence shield would destroy the strategic balance in Europe, CNN reported.
The US contended that the developments are directed against ballistic missile threats outside the Euro-Atlantic area and not meant to counter any missile threat from Russia.