Minister of Defense of Montenegro Milica Pejanovic and Foreign Minister of Montenegro Igor Luksic and NATO Secretary General Jens Stoltenberg

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NATO ministers have invited Montenegro to become the alliance's 29th member, the organization's first expansion in six years.

Foreign ministers extended the invitation to begin "accession talks" to Montenegro at a meeting in Brussels Wednesday.

Secretary General Jens Stoltenberg called the move a “historic decision” and said it affirmed NATO’s “open-door policy," Bloomberg reported.

Full membership for the former Yugoslav republic could take up to two years.

Bay of Kotor in Montenegro

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Balkan states Croatia and Albania were the most recent countries to join the U.S.-led military alliance in 2009.

The move could anger Russia who have stated their opposition to the plan before. Last year, Russia's foreign minister Sergei Lavrov said allowing Montenegro to join Nato would be a “provocation” and “irresponsible”, the Telegraph reported.