Russia President Vladimir Putin has warned that his country will to move its missiles closer to Europe in response to NATO "expansion" plans.
In a television interview to be broadcast later on Monday, Mr Putin said he was "concerned" about what NATO is doing.
He said: "Why are we reacting to NATO expansion so emotionally? We are concerned by NATO's decision-making."
Russia is to deploy its S-400 air missile defence system and ballistic Iskander missile in the Russian region of Kaliningrad, according to the country's RIA news agency.
Kaliningrad is separated from mainland Russia by borders with Poland and Lithuania.
Vikto Ozerov, head of the defence committee in the upper house of parliament, was reported as saying Russia sees the deployment as a response to the US setting up a missile shield in Europe.
Jens Stoltenberg, NATO's Secretary General, said: "Everything NATO does is defensive, proportionate and fully in line with our international commitments.
"Before Russia's aggressive actions in Ukraine, NATO had no plans to send troops to the Eastern part of our alliance.
"NATO's aim is to prevent a conflict, not to provoke a conflict.
"Moreover, we firmly believe and we are firmly committed to a two-track approach to Russia; strong defence, coupled with meaningful dialogue."
Mr Putin shared an apparently frosty handshake with Barack Obama at the beginning of the Asia-Pacific Economic Co-operation summit (APEC) in Lima at the weekend.
The White House said that the two discussed Ukraine and Syria during their four-minute conversation, with Mr Obama encouraging Mr Putin to stand by the agreement made in Minsk that was aimed at ending the Ukraine conflict.
He also called for US Secretary of State John Kerry and Russia's Foreign Minister Sergei Lavrov to continue working with other countries to solve the war in Syria.
Mr Putin said after the summit that both leaders had acknowledged that dialogue between their countries "was hard" but said he would be happy to see the outgoing US President in Russia.
He also spoke of his Mr Obama's successor Donald Trump, saying that the two share an interest in "normalising relations", adding that there was a big difference between "(Mr Trump's) pre-election rhetoric and actual policy".