The French police arrested 101 Romani fans, some with weapons, in Nice on Tuesday, a day before the teams gathered in the Europa League, the local prefecture announced.
A separate source said AFP that the Italian followers carried sticks, shovels and caspados around the city center in the French Riviera.
The Prefecture said that more than 400 police officers will be present for the group phase party on Wednesday.
“Since yesterday, more than 200 people, including two mobile units, deployed in the center of the city of Nice to prevent all kinds of public disorder and continued with the arrest of 102 people identified as Rome Ultras, carrying weapons,” he said Wednesday, before reviewing the number of arrests to 101.
“These people were arrested in police custody,” he added.
Local authorities have banned Romani fans to show visible signs of their loyalty in the city between 1300 GMT (6pm PKT) on Tuesday and 1000 GMT (3pm PKT) on Thursday.
