France's interior minister says 557 "violent supporters" have been arrested so far at the European Championship, and 344 of them were held by police.
Bernard Cazeneuve said custody has been followed by "very firm prison sentences for a certain number" of them.
In a statement, the government later said that 21 fans have been sent to jail and another six have been given suspended prison sentences. French authorities have ordered a further 25 supporters to be deported.
Trouble flared in Marseille during the opening days of Euro 2016, when England fans, Russian supporters and local youths clashed with each other and French riot police. Tear gas and water cannons were used to break up the trouble.
The hooligan threat at Euro 2016 comes amid heightened security in France after the Nov. 13 attacks in Paris, which claimed 130 lives.