Russian ally Serbia took the delivery of a sophisticated Chinese anti-aircraft system in a veiled operation this weekend, amid Western concerns that an arms buildup in the Balkans at the time of the war in Ukraine could threaten the fragile peace in the region.

The Chinese missile system has been widely compared to the American Patriot and the Russian S-300 surface-to-air missile systems although it has a shorter range than more advanced S-300s. Serbia will be the first operator of the Chinese missiles in Europe.

There are fears in the West that the arming of Serbia by Russia and China could encourage the Balkan country toward another war, especially against its former province of Kosovo that proclaimed independence in 2008. Serbia, Russia and China don’t recognize Kosovo’s statehood, while the United States and most Western countries do.