One person was seriously wounded by gunfire and six policemen were hurt in clashes between Croat football fans and Muslims in the Bosnian city of Mostar.
The rioting erupted in the ethnically divided city after Croatia lost 1-0 to Brazil in the World Cup.
Police said a large group of Croat fans smashed cars and the windows of nearby buildings in a city square, which was a frontline in the 1990s Bosnia war.
A group of Bosnian Muslims confronted the Croats and police intervened.
Mostar saw fierce fighting between Bosnian Croats and Muslims in 1993.
Most Bosnian Croats see neighbouring Croatia as their homeland and support the Croatia national team, correspondents report.
Police said there was considerable damage in the overnight violence and 26 people were arrested.