Vandals have desecrated 148 Muslim graves in France's biggest WWI cemetery, officials have said.
A pig's head was hung from one headstone and slogans insulting Islam and France's Muslim justice minister were daubed on other graves.
President Nicolas Sarkozy condemned the attack as a "hateful act" and the "most inadmissible kind of racism".
About 78,000 colonial subjects of France, including many Muslims from North Africa, died in the war.
The Notre Dame de Lorette war cemetery, near Arras in northern France, is on the site of some of WWI's largest battles.
About 100 police officers have been sent to the cemetery to investigate the incident.
President Sarkozy has called for the rapid detention and punishment of those responsible.
In a similar attack in April 2007, Nazi slogans and swastikas were painted on about 50 graves in the Muslim section of the cemetery. Two men were sentenced to a year in prison for that act.