Red tape police seals and a photograph are seen on the front door of the apartment of Mireille Knoll in Paris. Picture: Clotaire Achi/Reuters

Paris - The mayor of Paris, Anne Hidalgo, has called on citizens to join a demonstration planned for Wednesday in protest at the killing of an 85-year-old Jewish woman who escaped the Holocaust.

President Emmanuel Macron and politicians from right and left alike have condemned the killing of Mireille Knoll in her eastern Paris apartment on Friday.

Two suspects have been placed under formal investigation on charges of anti-Semitic murder and aggravated theft, according to a judicial source.

The two, born in 1989 and 1996, have both been remanded in detention, the source said.

In 1942, Knoll had narrowly escaped a notorious wartime round-up of Paris Jews who were deported to Nazi death camps, family lawyer Gilles-William Goldnadel told broadcaster BFMTV.

Her son Alain Knoll told the broadcaster that she had lived all her life in the eastern 11th arrondissement (district) of Paris.

According to French Jewish umbrella organization CRIF, Knoll's body was found after a fire at her apartment, but an autopsy revealed knife wounds.

READ: Anti-Semitism blamed for Holocaust survivor's horrific death

On Tuesday the door of her apartment was sealed by police tape, but a photo of the victim had been stuck to it. A smell of smoke still lingered in the air.

"My mother never did anyone any harm," Alain Knoll said. "And then, she was an 85-year-old lady who had lived her life trying to make the most out of what life could give her because she had suffered during the war ... She loved life."

"I call on all Paris' elected representatives, all Parisians, to take part in the march in white on Wednesday in homage to #MireilleKnoll," Hidalgo wrote on Twitter.

Macron's centrist La Republique en Marche and parties from the left and right of the political spectrum also called on their members to join the silent protest in white colours, announced by CRIF.

"The safety of French Jews is no longer guaranteed as it should be today," CRIF president Francis Kalifat told broadcaster i24 News.

Jews had become "a particular target" in the terrorist attacks that have hit France in recent years, and were also suffering from "an anti-Semitism that expresses itself with the greatest violence," Kalifat warned.

Overnight, Macron added his voice to the condemnations of the attack, describing it as a "horrific crime."

"I reaffirm my absolute determination to fight against anti-Semitism," he wrote on Twitter.

In recent years, French Jewish groups have repeatedly denounced anti-Semitic attacks.

Tensions around the Israeli-Palestinian conflict, as well as anti-Semitic propaganda by some Islamist preachers and media, are widely seen as playing a role.

The killing of Knoll came a month after a judge decided to treat the murder of a retired Jewish schoolteacher in Paris last April as anti-Semitic, after a long campaign by community groups.

Sara Halimi was allegedly thrown to her death from her third-floor apartment at the end of a frenzied attack by a young neighbour, according to press reports and her family's lawyers.

The French Interior Ministry recorded 311 anti-Semitic incidents in 2017, down from 335 in 2016 and 800 in 2015.

But outright anti-Semitic violence rose from 77 incidents in 2016 to 97 in 2017.

The figures show that France's Jewish community suffer a disproportionate burden of recorded hate crime - 311 out of an overall total of 950 incidents even though they probably amount to less than 1 per cent of the population.

France is thought to have the third-largest Jewish population in the world, after Israel and the United States, although no official figures are kept on citizens' religious or ethnic background.