US Patriot missiles have arrived in Poland as part of a deal to upgrade the NATO nations air defences.
The surface to air battery manned by some 150 American troops will be stationed just 80 kilometres from the Russian enclave of Kaliningrad on a rotating basis.
Moscow has criticised the move, saying it breaks trust and jeopardises regional security. But, Poland says the battery poses no threat to Russia.
The arrival of the missiles comes amid fresh efforts by Moscow and Warsaw to improve ties after April’s plane crash which killed Poland’s President Lech Kaczynski and dozens of other senior officials.