Montenegro began its first round of NATO membership talks on Monday, two months after the former Socialist republic was invited to join the military alliance, in a move that could further aggravate Western tensions with Russia.
The two-day talks cover political, military and legal aspects of Montenegro's accession, the alliance said in a statement. In a next move, the former Yugoslav country will be cleared to attend NATO meetings as an invitee, before becoming a fully fledged member.
Podgorica's ambassador to NATO, Dragana Radulovic, called Monday's talks a mark of the "progress made by Montenegro since regaining its independence."
But Moscow has accused NATO of conducting an expansionist policy that is threatening geopolitical stability.
Relations between NATO and Russia have deteriorated over the last two years, in large part due to Moscow's actions in Ukraine, where it is accused of supporting pro-Russian separatists and has annexed the Crimean peninsula.
"We have slipped into a period of a new Cold War," Russian Prime Minister Dmitry Medvedev told diplomats and defence officials at a meeting in Munich on Saturday, adding that "NATO's political course remains unfriendly and closed towards Russia."
He later backtracked partially from the remark, telling Time magazine in an interview that NATO's actions are "pushing us towards the emergence of a new Cold War."
"I never said that a new Cold War has started," he added.
EU foreign policy chief Federica Mogherini also played down the comment. "I have not seen a climate of Cold War in these last days," she told journalists in Brussels, ahead of a meeting Monday of the bloc's foreign ministers.
But Lithuanian Foreign Minister Linas Linkevicius was sharply critical of Russia's stance in its western neighbourhood, as well as in Syria, where Moscow is accused of militarily supporting the regime of President Bashar al-Assad.
"It's not a Cold War," Linkevicius said. "It's a hot war what's taking place now, as we speak. Not only in Syria, also in Ukraine."