French investigators are flying to Ivory Coast to hunt for the alleged ringleader of a gang suspected of torturing and killing a Jewish man.
Halimi is believed to have been held on a housing estate
The suspect, 26, of Ivorian origin, is believed to have fled France before police made several arrests last week.
Ilan Halimi, 23, died on his way to hospital after being found naked, bound and gagged in a Paris suburb. He had been held for ransom for three weeks.
French ministers believe he may have been a victim of anti-Semitism.
More than 1,000 people, mostly Jews, marched in Paris on Sunday to protest against the killing, which has shocked France.
Mr Halimi, a 23-year-old phone salesman, went missing on 21 January after a date with an unknown woman, who approached him at his workplace in central Paris.
He was dumped near the Sainte-Genevieve-des-Bois train station near Paris on 13 February, and found lying in agony with horrific injuries to his body. He died on the way to hospital.
'Brains of the barbarians'
He is thought to have been held on a housing estate in Bagneux, in the Paris suburbs.
His family were sent ransom demands by e-mail and text messages from the kidnap gang, whose leader called himself "brains of the barbarians".
Prosecutors initially ruled out anti-Semitism, saying the gang - believed to be behind six other botched kidnappings - were unemployed and motivated by money.
But Prime Minister Dominique de Villepin told a meeting of Jewish community leaders on Monday that the judge handling the case was investigating leads pointing to an anti-Semitic attack.
"We will do everything we can to arrest the authors of this barbarous crime and bring them to justice," he added.
Justice Minister Pascal Clement said one of the suspects had made it clear he had attacked Ilan Halimi "because he was Jewish, and Jews are rich".
Arrest warrants have been issued for the alleged leader, Yussef Fofana, and two women believed to have acted as bait for the kidnap targets.
Fifteen people, aged 17 to 32, were arrested last week in connection with the death. Five have since been released.