Two suspects have been given preliminary charges of murder with anti-Semitic motives over the death of an elderly Jewish woman, a French judicial official said.
Leading Jewish group CRIF said 85-year-old Mireille Knoll was killed last week in Paris' eastern 11th district.
She had been stabbed several times and her apartment set on fire.
Ms Knoll had reportedly escaped a notorious World War II round-up in Paris of Jews, who were then shipped to Auschwitz.
A silent march will take place on Wednesday in Paris in memory of Ms Knoll.
French President Emmanuel Macron tweeted that it was a "horrific crime", and reaffirmed his "absolute determination to fight against anti-Semitism".
J’exprime mon émotion devant le crime épouvantable commis contre Mme Knoll. Je réaffirme ma détermination absolue à lutter contre l’antisémitisme. https://t.co/FcSb1gqkQo— Emmanuel Macron (@EmmanuelMacron) March 26, 2018
France's government presented a plan earlier this month to better fight against racism and anti-Semitism, focusing on social media and prevention in schools.
The government notably wants to change French law to force internet platforms to detect, signal and remove illegal content.
An annual national count of racist, anti-Semitic, anti-Muslim and anti-Christian acts - mainly threats - dipped in 2017 compared with the year before.
However, anti-Semitic violence increased by 26%, and criminal damage to Jewish places of worship and burials by 22%.