NATO on Sunday harshly criticized Russia for placing a nuclear capable Iskander missile system in its exclave of Kaliningrad, which lies sandwiched between NATO members Poland and Lithuania.
"The deployment of missiles close to alliance borders that can carry nuclear warheads does not help to lower tensions," a NATO spokesman told dpa.
"We need more – not less – transparency and predictability on military activities to avoid incidents and the risk of misunderstandings," he said.
Russia admitted on Saturday that for training purposes it had placed Iskander missiles armed with nuclear warheads in Kaliningrad, which was known in Prussian times as Koenigsberg.
Lithuanian Foreign Minister Linas Linkevicius said that he suspected that the Russian move is a reaction to the beefing up of NATO defence capabilities in the region.
The alliance decided in the summer to send large numbers of troops to the Baltic States and Poland, which feel increasingly under threat of attack by Russia since it annexed Ukraine's Crimean peninsula in 2014.