UPDATE: 7:16 a.m. EST -- Montenegro's prime minister said NATO's invitation to the country to become part of the alliance was a "historic" day, the Associated Press reported.

"This is a crown jewel of the long-standing national efforts and comprehensive reform processes launched in 2006," Milo Djukanovic reportedly said.

Original story:

NATO has invited Balkan country Montenegro to join the military alliance led by the U.S. with Russia threatening retaliation over the move Wednesday. The invite is the coalition's first expansion in six years and Moscow had earlier called the bloc's extension plans to the Balkans a "provocation."

Diplomats from NATO said, according to Reuters, that the alliance would send a message to Russia that it does not have a veto on NATO’s expansion toward eastern Europe. Accession talks are expected to take a year, and once completed, the country will become the 29th member of the bloc.

Montenegro has a population of 650,000 and a military with 2,000 active members, the BBC reported. The country got its independence in 2006 from the erstwhile Yugoslavia, a long-time Russian ally.

On Wednesday, Kremlin spokesman Dmitry Peskov threatened retaliatory measures over the coalition's invitation to the Balkan country. "Moscow has always noted at various levels that the continuing expansion of NATO and NATO’s military infrastructure to the East, of course, cannot but lead to response actions from the East, namely, the Russian side in ensuring security interests and supporting the parity of interests," Peskov said, according to Russia's Tass news agency.

Russia’s chairperson of the Federation Council’s Committee on Defense and Security, Viktor Ozerov, also said Wednesday that if Montenegro joins NATO, Moscow will cancel programs for military and technical cooperation with the country. "Montenegro should recognize that a lot of programs that have been previously realized by it with Russia, including the ones in military and technical cooperation, will be impossible in the context of its NATO accession," Ozerov said, according to Sputnik News.

Meanwhile, NATO Secretary General Jens Stoltenberg called the invitation a "historic decision" and said, in a NATO statement, that the decision was "an important step in the Euro-Atlantic integration of the entire Western Balkans region and it makes clear that NATO keeps its door open, to complete our vision of a Europe whole, free and at peace."

He also said that the decision showed Montenegro’s "unwavering commitment to our common values and to international security," adding that it was important to continue Montenegro's work "on defense adaptation, on domestic reform, especially rule of law, and to continue to make progress in demonstrating public support for Montenegro’s NATO membership."

Another report by Tass cited Stoltenberg as saying that the alliance has also decided to resume the process of convening NATO-Russia Council meetings, which were cancelled after the 2014 Ukraine crisis and Moscow's annexation of Crimea. "We decided also to keep at the same time channels for political contact open. And the NATO Russia Council is part of these channels for political contact and dialogue... And I will now explore how we can use the Council as a tool for political engagement. We have never decided to not use it. And I welcome the support to then convene a Council, and we will look into how we can do that. I will do that together with the ambassadors, and I will come back on when and how this can be done," Stoltenberg said.

NATO's decision over the meetings with Russia follows Russian Foreign Minister Sergey Lavrov’s earlier comments that the relationship between Russia and Western powers were gradually improving.

U.S. Secretary of State John Kerry congratulated Montenegro on the invite from NATO in a tweet.