NATO will formally invite Montenegro to join the military alliance, diplomats told reporters in Brussels where foreign ministers have gathered for a two-day summit.

It would be the Western alliance’s first expansion since 2009 when Albania and Croatia joined.

NATO’s Cold War rival Russia has said it would regard Montenegro’s accession as a provocation.

But the United States expressed support. “We believe Montenegro’s membership in NATO will contribute to Balkan and European security,” a State Department spokeswoman said in Washington DC.

If things go according to plan, Montenegro would join at a summit in Warsaw next year.

Russian-backed opposition?

Radio Free Europe/Radio Liberty reports that pro-Russian opposition parties in the Balkan nation of 600,000 are accused of stoking unrest in an attempt to derail the NATO process. Demonstrators are calling on Prime Minister Milo Đukanović of the pro-Western Democratic Party of Socialists to step down.

Đukanović, who has featured prominently in Montenegrin politics since Yugoslavia fell apart in the early 1990s, insists that Russia’s hand is behind the protests.

Opposition parties deny any Russian involvement while Moscow accuses Đukanović of “demonizing” Russia.

Ethnic split

There is genuine skepticism about joining NATO, polls show, and much of it is concentrated in the country’s ethnic Serb minority. NATO’s 1999 bombing of Serbia — when Montenegro was still in a federation with it — as well as the Montenegrin split from Serbia in 2006 still divide public opinion.

Russia has traditionally looked on the Serbs as a brotherly Slavic people and maintained close relations with Belgrade.