REDZIKOWO, Poland: Poland on Friday broke ground on the northern section of a US missile defense shield launched in Romania a day earlier, which Russia slammed as a serious security threat despite US assurances to the contrary.
"Although we joined NATO years ago, now we are seeing that NATO is truly entering Poland," Polish President Andrzej Duda said before ceremony participants took shovels in hand and began digging at the Polish air force base.
Located in Redzikowo, northern Poland, and Deveselu in southern Romania, the two missile interceptor stations are part of NATO's larger European shield, due to become fully operational by 2018.
US and NATO officials insist the system is intended to counter the threat of short- and medium-range ballistic missiles, particularly from so-called "rogue" states the Middle East like Iran.
But with the Redzikowo station just 250 kilometers (155 miles) from the Russian enclave of Kaliningrad, Moscow views the system as a security threat on its very doorstep.
President Vladimir Putin on Friday warned Washington that Russia will consider measures to "end threats" from US anti-missile systems in Europe but said Moscow would not be engaged in a new arms race.
US Deputy Secretary of Defense Robert Work was on hand Friday for the start of construction on the Aegis Ashore-type missile defense facility in Redzikowo.
It will include 24 land-based SM-3 missiles as well as anti-aircraft systems.
The facility in Poland "is a US contribution to NATO missile defence," Work said at the ground-breaking ceremonies, adding that "when completed in 2018 it will be capable of defending the central and northern arc of NATO."
Work also said that "by the (NATO) Warsaw summit in July, we expect alliance leaders to declare initial operational capability for the NATO ballistic missile defense system."
Launched in 2010, NATO's anti-missile shield system -- based essentially on US technology -- involves the progressive deployment of missile interceptors and powerful radar in eastern Europe and Turkey.
NATO and the United States said this spring that they will switch their defense doctrine from assurance to deterrence in Eastern Europe in response to a "resurgent and aggressive Russia" following its 2014 annexation of Crimea from Ukraine.
The Pentagon said in March it would begin continuous rotations of an additional armored brigade of about 4,200 troops in Eastern Europe beginning in early 2017.
Spooked by Russian action toward Ukraine, eastern NATO members including the formerly Soviet-ruled Baltic states and Poland have lobbied the alliance to increase its presence in the region to guarantee security.