The presence of Serbian officials at the funeral of war criminal Ratko Mladic was "deeply regrettable", EU chiefs Ursula von der Leyen and Antonio Costa said Tuesday.
Serbia's commemoration of the so-called "Butcher of Bosnia" -- who was buried Monday in a service attended by thousands -- has put Brussels on a collision course with Belgrade, which is a candidate country to join the EU.
Several Serbian ministers including the defence and justice ministers attended, alongside Russia's ambassador to the country, a string of top officials from the Bosnian Serb entity including its President Sinisa Karan, and his predecessor Milorad Dodik.
"The images from Ratko Mladic's funeral yesterday in Belgrade were shocking," European Commission president von der Leyen and European Council boss Costa wrote online.
"The elements of official support and the presence of some senior Serbian officials at the funeral are deeply regrettable."
The pair said the move demonstrated "a failure to confront a dark chapter in Europe's recent history and contradict the values underpinning Serbia's path towards the European Union."
Mladic died in The Hague last month, aged 84, after being convicted of genocide, war crimes and crimes against humanity committed during the 1990s Bosnian war.
Serbian Justice Minister Nenad Vujic initially announced "military and state honours" for Mladic, triggering international outrage, before President Aleksandar Vucic tempered the decision.
Vucic has rejected accusations of glorifying the former general, describing the service as in keeping with the family's wishes.
The EU has yet to say what the consequences could be for Serbia's efforts to join the 27-nation bloc.
The EU's enlargement chief Marta Kos already scrapped a visit to Belgrade and it looks likely von der Leyen will skip Serbia on an upcoming tour of the Balkans.
