Australian Open organizers issued a reminder to players and their entourages about their policy on «inappropriate flags» after video surfaced showing Novak Djokovic’s father posing for photos with fans holding Russian flags.

Victoria Police questioned four fans with «inappropriate flags and symbols» after Wednesday’s quarter-final match between Djokovic and Russia’s Andrey Rublev.

A video also posted on social media showed a supporter on the steps of the Rod Laver Arena holding a Russian flag with the image of President Vladimir Putin.

Late on Wednesday, another video showed Djokovic’s father, Srdjan, posing for photos with fans holding Russian flags.

«Players and their teams have been informed and reminded of the event’s policy regarding flags and symbols and to avoid any situation that has the potential to be disruptive,» Tennis Australia said in a statement on Thursday.

“We continue to work closely with law enforcement and event security agencies.”

The flags of Russia and Belarus are banned from Melbourne Park during the tournament after a complaint from the Ukrainian ambassador to the country.

Belarus is a key arena for Russia’s war in Ukraine, which Moscow calls a «special operation.»

Photos on social media also showed a fan in the crowd during Wednesday’s match wearing a «Z» on his jersey.

Russian forces have used the letter «Z» as an identification symbol on their vehicles in Ukraine after the invasion. Some supporters of the invasion have also used the poster.

Russian and Belarusian players were banned from Wimbledon last year but can compete as individual athletes with no national affiliation at Melbourne Park.

Their flags are not displayed next to their names on television broadcasts, as is the case with other players, and their nation is not indicated on the draw sheets.