BRUSSELS — Montenegrin officials say that despite the fierce objections of Russia, they are optimistic that their country will be invited to join NATO, possibly by the end of this year.

Its accession to the Western military alliance would mark the first expansion of NATO's ranks in ex-Communist Eastern Europe since Montenegro's neighbours, Albania and Croatia, joined in 2009. It also would become the first new addition to NATO since relations between Russia and the West cooled over Russia's intervention in Ukraine's 2014 revolution and the ongoing bitter conflict there which is still ongoing.

One Brussels-based diplomat said Montenegro's accession would send a message to Moscow that it "cannot halt NATO's expansion."

Ambassadors of NATO's North Atlantic Council met in Montenegro's capital, Podgorica, on Thursday in what some see as the latest signal of NATO's resolve to usher the tiny Adriatic republic of 650,000 people into its ranks.

The US has signaled its support for the accession of the former Yugoslav republic, and Montenegrin Foreign Minister Igor Lukšić said he believes the conditions exist for NATO's 28 members to decide, perhaps as soon as December, to invite Montenegro to join.

However, a NATO source said that any invitation would depend on Montenegro making further progress on reforms to tackle corruption and improve the rule of law, and ensuring public support in the country, where opinion polls suggest only a narrow majority support entering NATO.

Many ethnic Serbs in Montenegro, like their kin in Serbia, fiercely oppose joining NATO. It was 16 years ago that NATO members struck targets in Montenegro during an 11-week air war to drive security forces under Serbian strongman Slobodan Milošević from Serbia's then-southern province of Kosovo.

Montenegro's accession would be much less contentious than earlier overtures by the West to the likes of ex-Soviet Georgia, but even so Russia has described NATO's extension into the Balkans as a "provocation."

However, Podgorica's relations with Moscow remain uneasy given the Montenegrin government's pursuit of closer integration within the West. Relations have further cooled in the wake of Montenegrin support of EU sanctions against Russia over Moscow's annexation of Crimea.

As well as Montenegro, all countries of the Western Balkans are moving toward EU membership, albeit at different speeds. Kosovo is at the very start of the negotiations on a sStabiliszation and Aassociation Aagreement (SAA) with the union while Croatia became a full EU member in July 2013.

Turkey, Macedonia, Montenegro, Serbia and Albania are candidate countries, whereas Bosnia and Herzegovina and Kosovo are considered potential candidates. EU membership negotiations started with Montenegro in 2012 and with Serbia in January 2014.