Demonstrators burned the EU and US flags during a protest against Kosovo's independence declaration in Athens on Saturday as hundreds of Serbs staged an anti-independence demonstration in the Swiss city of Zurich.
About 1,000 people took part in the Athens rally organised by the Greek communist party (KKE), police said.
The demonstrators chanted "NATO and the European Union out of the Balkans" as they marched to the EU mission and the US embassy which were protected by large numbers of police.
They burned the EU flag outside the European mission and US flags outside American embassy before dispersing peacefully.
Greece, an EU member, has not yet indicated whether it will recognise Kosovo's February 17 declaration of independence. Switzerland could announce this week whether it is to recognise Kosovo and about 1,000 people, mainly Serbs, took part in the Zurich rally.
Pro-Serb groups have also called for a rally tomorrow outside the UN headquarters in Geneva.