The United States has broken ground on a military installation in Poland that will form part of NATO's larger European missile shield.
Washington has said the shield is to protect NATO from short- and medium-range missiles, particularly from the Middle East.
Russia adamantly opposes the missile-defense network, asserting that its true aim is to undermine Russia's nuclear deterrent and upset the regional strategic balance.
Russian President Vladimir Putin warned on May 13 that U.S. antimissile systems in Europe will "force" Moscow "to consider putting an end to the threats emerging in relation to Russia's security."
However, Putin said that Russia would not be involved in a new arms race.
On May 12, the United States activated a first-of-its-kind ground-based missile-interceptor site in Romania, despite Moscow's protests.
INFOGRAPHIC: European Missile-Defense System
Work on the site in Redzikowo in the north of Poland is to be completed at the end of 2018.
Situated some 250 kilometers from the Russian exclave of Kaliningrad, it will host 24 land-based SM-3 missiles as well as antiaircraft systems.
The installation in Poland is final site of the European missile shield, which will be handed over to NATO in July and run from a U.S. air base in Germany.
