Speaking in Bucharest, Assistant Secretary of State Frank Rose told a news conference that turning on the defense shield did not represent a security threat to Moscow, despite the Kremlin's concerns. The site is set to go live on Thursday, DW reports.

"Both the U.S. and NATO have made it clear the system is not designed for or capable of undermining Russia's strategic deterrence capability," Rose told reporters.

Read alsoU.S. begins works on Poland's Redzikowo missile defense shield"Russia has repeatedly raised concerns that the U.S. and NATO defense are directed against Russia and represents a threat to its strategic nuclear deterrent. Nothing could be further from the truth."

Work on the Deveselu station, in the south of Romania, began in October 2013 and is estimated to have cost some $800 million (EUR 700 million).

Read alsoRussia to set up three divisions to counter NATO — Defense chiefThe station will be equipped with a battery of SM-2 missile interceptors and will be officially inaugurated into the NATO missile defense shield at the organization's summit in Warsaw in July.

Douglas Lute, the U.S. ambassador to Romania, said the new station was an important part of Article Five of a NATO pact in which all 28 members are bound to come to each other's defense in the case of a military threat.

Read alsoU.S. sends F-22 fighters to reassure NATO allies facing Russia: Reuters"Tomorrow is a demonstration that the U.S., Romania and the other allies contributing to the defense system mean what Article Five says," he said.

In spite of repeated assurances, the Kremlin maintains that the real purpose of the defense shield is to provide the U.S. with enough military might to neutralize Russia's nuclear arsenal in order to make the first strike, in the event a war breaks out.