The Kremlin accused NATO on Tuesday of treating Russia like an "enemy" and said it would closely follow any decisions taken at a two-day summit of the Western military alliance and respond with unspecified measures to protect its own security, Reuters reports.
NATO Secretary-General Jens Stoltenberg said earlier he expected its leaders gathering in Vilnius to send a "positive message" to Ukraine about its path to eventual NATO membership.
Moscow has cited NATO's eastern expansion as a key factor in its decision to invade Ukraine nearly 17 months ago.
"Russia is perceived by them (NATO leaders) as an enemy, as an adversary. It is in this vein that the discussions (in Vilnius) will be conducted," Kremlin spokesman Dmitry Peskov told a regular news briefing.
"We are monitoring this very carefully because much of what has been said will be subject to in-depth analysis in order to take measures to ensure our own security," he added.
Foreign Minister Sergei Lavrov, in separate comments, said Moscow was taking "appropriate" measures in anticipation of NATO's further expansion. He did not elaborate.
NATO leaders at the summit in the Lithuanian capital are set to approve the alliance's first comprehensive plans since the end of the Cold War to defend against any attack by Moscow.
Diplomats also said differences were narrowing among the allies over Ukraine's push for NATO membership, although Kyiv will not be invited to join while war still rages on its territory.
