• The Western Balkans, a group of six countries that EU officials have repeatedly said belong to the European family, comprises Albania, Bosnia and Herzegovina, Montenegro, Kosovo, North Macedonia and Serbia.
• Concerns over Russia's influence in the Western Balkans — an area still scarred by the ethnic wars of the 1990s — have intensified since Moscow's full-scale invasion of Ukraine.
• "It is clear that the Russian invasion of Ukraine affects the stability of our vulnerable partners and expose them to a greater risk of malign influence," a NATO official told CNBC.

As Russia's onslaught in Ukraine approaches its one-year milestone, fears are growing about the Kremlin's efforts to leverage simmering tensions in a "second battleground."

The Western Balkans, a group of six countries that European Union officials have repeatedly said belong to the European family, comprises Albania, Bosnia and Herzegovina, Montenegro, Kosovo, North Macedonia and Serbia.

Not yet members of the 27-nation bloc, the region of roughly 18 million in Southern and Eastern Europe is known as an arena of geostrategic rivalry, with Moscow, Brussels and Washington among those jockeying for influence.

The promise of EU accession is viewed as the West's most powerful tool to stabilize and integrate the region, and Western Balkan leaders have recently welcomed what appears to be a new mindset to strengthen ties.

But concerns over Russia's influence in the Western Balkans — an area still scarred by the ethnic wars of the 1990s — have intensified since the Kremlin's full-scale invasion of Ukraine.

Speaking at the World Economic Forum in Davos, Switzerland, North Macedonia President Stevo Pendarovski said that, aside from Kyiv, he believed that the Western Balkan region was the "soft spot" of Europe's security architecture.

NATO, which counts Albania, Montenegro and North Macedonia among its members, said it has observed cyberattacks, disinformation, intimidation and other destabilizing activities in the Western Balkans in the past 12 months. This is in addition to recurring regional tensions, including in Kosovo and Bosnia and Herzegovina.

The U.S.-led military alliance also warned of foreign actors working to undermine progress, while North Macedonia's Pendarovski says that the Western Balkans has been targeted by Russia's divisive agenda for several years.

"My judgment is that, if Russia will try to deflect somehow the attention of the West from Ukraine, which is the main theater of war and propaganda of course, that the Western Balkan region is more prone to that than the Baltics. So, we should take care about that," Pendarovski said last month.

"It seems to me that the so-called soft spot in the whole pan-European security architecture right now, apart from Ukraine of course … is the Western Balkans."

'A second battleground for Russia'

Russia is said to resent the pursuit of Western Balkan countries for integration into the EU and NATO, and the Kremlin is accused of working to leverage ethnic and religious fault lines to undermine those efforts.

Moscow, which has long cultivated ties with Serbia and other allies, has denied claims that it is seeking to sow chaos across the region.

Adnan Ćerimagić, a senior analyst for the Western Balkans at the European Stability Initiative think tank, said he agreed with Pendarovski's security assessment of the region amid Russia's war in Ukraine.

"The reason why I would agree is that like in Russia, in the Western Balkans, there is a political vision that does not align with the current shape of [its] borders," Ćerimagić told CNBC via telephone.

Ćerimagić said Russia's war in Ukraine provides Europe with a clear opportunity to cement stability in the Western Balkans. He said the bloc could seize this moment by providing a concrete offer to the countries, allowing them to join by 2027 or 2030, if they implement the necessary reforms.

"I think if they want to seal the deal, they will need to step up their offer to the region," Ćerimagić said.

EU officials have sought to reaffirm the importance of bringing the Western Balkans into the bloc since Russia's invasion of Ukraine, and regional leaders — in a stark change of tone from just a few months prior — lauded this development late last year.

At the EU-Western Balkans summit in early December, which was hosted in the Balkan region for the first time, the bloc underscored its "full and unequivocal commitment to the European Union membership perspective of the Western Balkans."

This was on the condition of "credible reforms" by partners.

Peter Stano, the EU's lead foreign affairs spokesperson, said he completely rejects criticism that the EU hasn't done enough to support the Western Balkan accession into the bloc.

"The fact that they are in the accession process means that every day they are getting closer and more integrated with the EU based on their efforts in implementing reforms and with substantial assistance from the EU," Stano said.

Asked about the current security situation in the region, Stano replied: "The issue is more about stability than the security as such."

"It is not a war zone, and it will not become a war zone for two reasons. Some of the countries in the region are NATO members already, and in others, we have EU missions (military and civilian ones) and all of them are in the EU accession process," Stano said.

"This provides enough preventative safeguards from any kind of hard or hot conflict to erupt," he added, noting there are still incidents and tensions, "but this is something different and linked to previous unresolved issues."

"For sure, the Western Balkans is a second battleground for Russia in terms of foreign interference and information manipulation. It has been before, but after Ukraine, this intensified in terms of overall interference, including cyberattacks, and trying to undermine the stability because [Russian President Vladimir] Putin doesn't want them to get closer to the EU," Stano said.

Future of the Western Balkans 'squarely within the EU'

For its part, NATO said that the group's Strategic Concept approved at the Madrid summit in June last year reaffirmed the strategic importance of the Western Balkans to the military alliance.

"It is clear that the Russian invasion of Ukraine affects the stability of our vulnerable partners and exposes them to a greater risk of malign influence," a NATO official told CNBC. "We will continue to work together to preserve stability, and support reform and resilience in the region, because security and stability in the Western Balkans is important for NATO and for peace and stability in Europe."

North Macedonia's Pendarovski last month described the U.S. as a "key player" in supporting Western Balkan countries through Russia's war in Ukraine.

In response to a request for comment, a State Department spokesperson told CNBC that Washington remains deeply engaged in the region, describing the future of the Western Balkans as "squarely within the EU."

"We must not let the Russian government use its war of choice to hold back the progress of the countries of the Western Balkans," the spokesperson said.

"Russia has demonstrated with exquisite clarity that it does not share the same values and is not looking out for their best interests," they added. "Russia's war has also clarified how urgent our work is to assist all the countries of the Western Balkans to fully advance democratic reforms and consolidation necessary to achieve their aspirations of integration into European and Euro-Atlantic institutions."