French President Jacques Chirac has condemned violence that led to the shooting of a French football fan by a plain-clothes police officer.
President Chirac said he was horrified by the reports of racism
The policeman fired into the crowd after he was physically attacked while seeking to protect a fan from anti-Semitic abuse, officials say.
The violence broke out after Israeli side Hapoel Tel Aviv beat Paris Saint Germain (PSG) 4-2 in a European match.
Mr Chirac said he was horrified by the reports of racism and anti-Semitism.
The BBC's Caroline Wyatt in Paris says the incident has shocked France and raised questions over racism, anti-Semitism and violence among football fans.
A hard core of PSG supporters are connected to the far right, she adds, with several fans banned from the club's matches after previous violent incidents.
Prosecutors have opened an inquiry into the incident, to determine whether the officer involved, Antoine Granomort, should face criminal charges, AFP news agency reported.
Mr Granomort reportedly fired tear gas, then live ammunition in an effort to disperse a fighting crowd near the Parc des Princes football stadium in Paris.
As a result, a 24-year-old PSG fan was killed and a 26-year-old man was seriously wounded. He remains in hospital in a serious condition.
French Tel Aviv fans were subjected to anti-Semitic abuse by PSG fans
According to Paris state prosecutor Jean-Claude Marin, young French fans of the Tel Aviv team were rounded on by PSG supporters chanting anti-Semitic slogans after the Paris side suffered defeat.
About 100 PSG fans gathered to chase one Tel Aviv supporter, the prosecutor said, at which point Mr Granomort, who is black, tried to intervene.
Witnesses said the crowd hurled racist insults at him, while making Nazi salutes and shouting anti-Jewish abuse at the man he was trying to protect.
According to the French authorities, Mr Granomort was physically attacked as he shouted that he was a police officer and pulled out his gun.
Fans interviewed on French radio said he had appeared to fire two shots in panic, as he was pushed to the ground.
He then sought refuge in a McDonald's restaurant with the man he had been trying to defend, while police reinforcements were brought in to restore calm.
Police union official Luc Poignant told the AFP news agency that Mr Granomort had "had no choice but to defend himself and protect another person".
Speaking at a summit meeting in Italy, Mr Chirac said the racist remarks reported "inspire a feeling not only of condemnation, not only of stupefaction - but also of horror".
French Prime Minister Dominique de Villepin called for new, tougher measures to deal with football hooligans.
Anti-racism groups called for urgent action to stamp out racist behaviour among football fans, a message echoed by Paris Mayor Bertrand Delanoe.
The head of the French football federation, Jean-Pierre Escalettes, told AFP the incident showed the need to "step up the fight against violence and racism, to wipe out this scourge that destroys the values of sport".