Montenegro sits between two NATO countries - Croatia and Albania. The Balkan nation was once part of the Federal Republic of Yugoslavia. It has a coast on the Adriatic Sea, which is home to deep-water harbours capable of porting big warships. The country had been one of Russia's allies in the Balkan Peninsular for decades.
But after it gained independence in 2006, the country started to seek NATO membership.
Analysts believe that if the country joins the organization, Russia's influence over the Balkan region would be weakened.