(ANSA-AFP) - BERLIN, 01 NOV - Germany has cautioned Serbia against cultivating deeper ties with Russia, warning that it could thwart its bid to join the European Union, a German government source said on Tuesday. Two days ahead of a Western Balkans summit in the German capital intended to bolster relations with the six countries of the region, the senior official said Belgrade needed to decide whose side it was on: Moscow's or the EU's. "The relationship with Serbia is complex -- there is light as well as shadows," said the source, who spoke on condition of anonymity. "Serbia's relations with Russia are certainly part of the shadows." The source said the German government had been, for example, "surprised and disappointed" when Serbian Foreign Minister Nikola Selakovic in September signed an agreement with his Russian counterpart Sergei Lavrov agreeing to confer on foreign policy. The German official said it was time for Serbian President Aleksandar Vucic to get off the fence. "If he takes the path to Europe, he will have support, from the EU as a whole and from the German government," the source said. "Should he choose the other path, it will have ensuing consequences" for Belgrade's future with the EU, the official said. (ANSA-AFP).