French police have arrested four youths in connection with the desecration of 148 Muslim graves in France's largest war cemetery.
A pig's head was hung from one of the several tombstones targeted by vandals who also wrote slogans insulting France's Muslim justice minister, officials said.
The youths are believed to belong to a neo-Nazi group which scrawled swastikas on 52 Muslim graves in the same cemetery in April last year.
The Notre Dame de Lorette cemetery, located in the town of Arras, commemorates troops who fought for control of northern France at the start of World War I.
'Profound outrage'
Describing Saturday's incident, Jean-Pierre Valensi, a state prosecutor, said: "The slogans directly target Islam and they gravely insult Rachida Dati, the justice minister [a daughter of North African immigrants]".
Inaugurated in 1925, the cemetery houses the remains of about 40,000 soldiers, half of them in named graves.
Saturday's attack targeted the Muslim quarter which includes 576 tombs that are grouped together and face Mecca.
Jean-Marie Bockel, the secretary of state for veteran's affairs, said the government will review security at Notre Dame de Lorette.
Around 100 French gendarmes have gathered evidence from the cemetery following the attack.
Nicolas Sarkozy, the French president, expressed "profound outrage" at the "sordid" attack and vowed that those responsible would be punished.
David Bardiaux, the curator of the cemetery's museum, said: "It is inadmissible, unbelievable. The cemetery is not locked, so it doesn't take courage to come and do this."