The Italians – five young men and one woman – allegedly set fire to a police van with an agent inside, who managed to escape.
They were also charged with belonging to a criminal group, public disorder and property damage.
A Spanish woman and a French woman were also arrested on Saturday and face the same charges.
Police have arrested more than 100 people since the protests over the jailing of rapper Pablo Hasél erupted on February 16.
The protests escalated on Saturday.
Hasél has been sentenced to nine months in prison after being convicted of glorifying terrorism and insulting the monarchy, galvanising defenders of freedom of speech and sparking protests.
He was convicted for lyrics and tweets that included references to Basque separatist group ETA, calling Spain’s former King Juan Carlos a mafia boss, and likening Spanish judges to Nazis.
The conviction also prompted the government to announce it would relax free speech legal restrictions.