NATO has formally invited the nation of Montenegro to join the military alliance, NATO Secretary-General Jens Stoltenberg announced Wednesday.

The move is likely to displease Russia, which views NATO expansion as a threat to its security.

Montenegro started on a path to join the alliance in 2009. The formal invitation marks the beginning of accession talks, NATO said.

Montenegro already supports NATO’s efforts in Afghanistan and has actively cooperated with the alliance in other ways.

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