Another British man was arrested on Thursday while attempting to leave the country.
The incident took place outside of Kalypso Club on Pag Island, while the house and techno event was taking place. Croatian media report that the fight erupted between two groups of tourists, and seven people are now in custody.
"Our thoughts and condolences are with the family and friends of the people affected," festival organizers said in a statement on Facebook today.
Update: Police arrested a 25-year-old suspect at the airport on Thursday in the coastal town of Split while he was attempting to leave Croatia.