Four people were being questioned by police after a Russia flag with Vladimir Putin's face on was displayed at the Australian Open.
A small group of people gathered outside Rod Laver Arena following Novak Djokovic’s quarter-final victory over Russian Andrey Rublev and were heard chanting "Serbia, Russia".
A man wearing a T-shirt bearing the pro-war Z symbol held up the Putin flag. A different man had been pictured with a Z T-shirt inside the stadium during the match.
A statement from Tennis Australia read: "Four people in the crowd leaving the stadium revealed inappropriate flags and symbols and threatened security guards.
"Victoria Police intervened and are continuing to question them. The comfort and safety of everyone is our priority and we work closely with security and authorities."
Organisers last week banned Russian and Belarusian flags from the venue for the duration of the tournament after one was held up at a match between Russian and Ukrainian players.