BRUSSELS (Reuters) - The Eurovision Song Contest's ban of the European Union flag was a "completely regrettable" mistake that should be rectified next year, the European Commission said on Monday.

The European Broadcasting Union (EBU), which operates Eurovision, said Swedish host broadcaster SVT chose to limit flags among participants and the audience at the venue in Malmo to those of the participating countries, along with the rainbow flag.

This meant the EU flag, often waved at the 2023 contest, was banned. Several attendees wrote on social media that security denied them entry with the flag.

The European Commission said flag of blue with 12 yellow stars was a flag for all EU members as well as being part of the symbol for the 46-nation Council of Europe stretching from Iceland to Azerbaijan.

"It is certainly completely regrettable that the flag of all the EU members taking part in the competition as well as other states belonging to the Council of Europe.... could not be shown," Commission spokesperson Eric Mamer said.

"We can certainly encourage the EBU to understand that this is a mistake and then it is their decision on how to proceed."

Margaritas Schinas, the Commission vice president overseeing culture, would raise the issue with EBU on Monday in what the spokesperson said was likely to be a "very lively discussion".

The EBU said that the flag policy was more rigorously enforced by security at this year's event due to heightened geopolitical tensions.

Several thousand demonstrators waving Palestinian flags gathered in central Malmo to protest against Israel's participation over the Israeli military campaign in Gaza.

"We will look again at the flag policy for 2025 in conjunction with our new host broadcaster SRG SSR," EBU said of the next contest, due to be held in Switzerland.

(Reporting by Philip Blenkinsop; Editing by Alex Richardson)