Germany fears Russia intends to block further European Union expansion into the Balkans, according to a confidential Foreign Ministry analysis seen by weekly Der Spiegel.

The magazine reports that German diplomats worry Russia is levering its influence in Bosnia and Herzegovina as well as Serbia with an eye toward preventing both countries from fully joining the West.

Russia has historically looked upon the Orthodox Christian and Slavic Serbs as a brotherly nation. Famously, it entered World War I in 1914 to defend Serbia against the Austro-Hungarian Empire and its German ally.

Last month, Russian president Vladimir Putin visited Belgrade where he reiterated his opposition to Kosovo’s independence. President Tomislav Nikolić, a Serbian nationalists, pledged not to bow to European pressure and join sanctions against Russia for its annexation of Ukraine’s Crimean Peninsula and continued support for separatists in that country’s southeast.

With the exception of Cyprus, Greece, Romania, Spain and Slovakia, all European Union member states recognize the largely ethnic Albanian Republic of Kosovo.

Although Serbia’s ruling Progressive Party is generally pro-European, its Socialist Party coalition partner — which was led by Slobodan Milošević during the 1998-1999 Kosovo War — still opposes Kosovar independence which would likely be a prerequisite for European Union membership.

Like many countries in Eastern Europe, Serbia is completely dependent for natural gas on Russia. It is also integral to Russia’s plans to build the South Stream pipeline across the region into Austria.

Neighboring Bulgaria, which joined the European Union in 2007, suspended its construction of the pipeline during the summer under pressure from Brussels.

Poland and Slovakia have both seen their supplies of Russian gas cut, apparently in retaliation for their support of economic sanctions against Russia.

Russo-Serbian ties go beyond energy. According to the German Foreign Ministry, Russia is engaging in “public diplomacy with clear pan-Slavic rhetoric” to sway Serbs — in Serbia as well as Bosnia where a third of the population is Serbian.

“One gets the impression that Russia is trying to gain influence over all of Bosnia-Herzegovina via the Serbian partial republic Srpska,” German agriculture minister Christian Schmidt, who recently visited the region, told Der Spiegel. “That also makes the path of neighboring Serbia into the EU more difficult.”

The region’s economic relations with Russia have deepened in recent years. Russian Railways, led by Putin ally Vladimir Yakunin — who was personally sanctioned by the United States after the Crimean invasion — is refurbishing rails in Serbia. Lukoil, Russia’s second largest oil producer, owns almost 80 percent of Serbia’s main petroleum company, Beopetrol. The energy conglomerate Gazprom, which is seen as particularly close to the Kremlin, holds majority ownership in the country’s largest natural gas supplier.

In Montenegro, another Serbian breakaway republic that is already on track to join the European Union, a full one third of companies is owned by Russians.

In August, German chancellor Angela Merkel convened a meeting of Balkan leaders in Berlin where she called for “speedy progress” in the accession of their countries to the European Union. “Slovenia and Croatia are already EU members,” she said, “and others have made quite considerable progress.”

However, corruption and political instability remain relatively high in some Balkan states and nearly all have unresolved ethnic conflicts stemming from the violent breakup of Yugoslavia in the 1990s, making their admission to the bloc problematic.

Moreover, many Western Europeans have tired of European Union expansion, lamenting the influx of cheap laborers from the former East Bloc.

Even if Bosnia and Serbia were to join the European Union, Russia could maintain its influence. As German conservative member of the European Parliament Elmar Brok, who chairs its Committee on Foreign Affairs, told Der Spiegel, “Putin’s goal is to exert so much pressure on Balkan states that they either back away from EU membership or that, once they become members, influence EU resolutions in a pro-Russian manner.”

Correction: An earlier version of this story omitted Cyprus and Romania from the list of European Union member states that do not recognize the Republic of Kosovo.