NATO has welcomed Montenegro into the alliance in its first expansion since 2009.
Alliance Secretary-General Jens Stoltenberg announced the invitation on Wednesday, the second day of a two day meeting of NATO foreign ministers.
The announcement sets in motion an accession process that will continue over months before Montenegro formally becomes the 29th member of the alliance, the first expansion since Albania and Croatia were admitted in 2009.
Russian Foreign Minister Sergei Lavrov said last September that any expansion was “a mistake, even a provocation.”
Many Western foreign ministers broke off formal contact with Russia in April last year after Moscow annexed Ukraine’s Crimea peninsula.