The European Union on Monday sent an official complaint to the broadcaster of the Eurovision song contest over its refusal to let participants wave the bloc's flag at this year's final.

"Such actions cast a shadow over what is meant to be a joyous occasion for peoples across Europe," European Commission vice president Margaritis Schinas wrote to the European Broadcasting Union (EBU). 

"With the EU being targeted by malicious and authoritarian actors, EBU's decision contributed to discrediting a symbol that brings together all Europeans."

He demanded the broadcaster "explain the rationale behind this decision and attribute responsibility where it is due".

"The incoherence in the EBU's stance left myself and millions of viewers wondering for what and for whom the Eurovision Song Contest stands," Schinas wrote. 

Switzerland's Nemo won the Eurovision Song Contest on Saturday, becoming the first artist identifying as non-binary to claim victory, in a competition marked by controversy over Israel's participation during the war in Gaza.

Twenty-five nations competed Saturday but much of the focus centred on the controversy of Israel being able to take part.

Organisers banned all flags other than those of the participating countries, but Nemo sneaked in an emblem representing non-binary people and displayed it during the show's introduction. 

The EU's 12-star flag is frequently flown by member states alongside their own at official buildings and events.  

The International Olympic Committee has allowed the flag to be displayed at venues and award ceremonies at the upcoming summer games in Paris.