PARIS, Sept. 16 (Xinhua) -- The French government announced Sunday that it intends to stand firm against illegal demonstration following Saturday's anti-American demonstration to protest against a controversial anti-Islam movie made in the United States.

French Interior Minister Manuel Valls told France 2 that "this event is unacceptable ... completely intolerable." He said he has given instructions to avoid such event to happen again, stressing that "these demonstrations are prohibited. Any hostility, appeals to hatred must be fought with the utmost firmness."

French Prime Minister Jean-Marc Ayrault also expressed the government's determination to get tough with illegal demonstrations while speaking to the French press.

According to local press, between 200 and 250 protesters staged demonstration near the U.S. Embassy in Paris on Saturday. One hundred and fifty-two people were detained and one has been placed in custody on suspicion of doing violence against police officers, in which four were slightly wounded.

French prosecutors are set to investigate how the demonstration was organized without proper permits. Investigations to identify the organizers of the event were also conducted on Sunday.