Nearly 100 graves at a Jewish cemetery in eastern France have been desecrated with swastikas.
The damage was discovered on Tuesday, ahead of nationwide marches against a rise in anti-Semitic attacks.
French President Emmanuel Macron visited the cemetery, in a village near Strasbourg, telling community leaders: "It's important for me to be here with you today."
France has the biggest Jewish community in Europe, about 550,000 people.
The damage was discovered on Tuesday in Quatzenheim, a village in Alsace close to France's border with Germany. Nazi symbols and anti-Semitic slogans were spray-painted on the graves.
One tombstone was defaced with the words "Elsässischen Schwarzen Wolfe" ("Black Alsatian Wolves"), the name of a militant far-right group active in the 1970s and 1980s.
The group burned down a museum at Natzweiler-Struthof - a former Nazi death camp - in 1976.
In a video statement, Israeli Prime Minister Benjamin Netanyahu condemned the "shocking" attack by "wild anti-semites."
"I call on the leaders of France and Europe to take a strong stand against anti-Semitism. It is a plague that endangers everyone, not just us," he said.
The attack came ahead of dozens of rallies against anti-Semitism scheduled to take place across France.
Tuesday's demonstrations are being organised by 14 political parties and are expected to take place in as many as 60 cities.
Is anti-Semitism on the rise in France?
Interior Minister Christophe Castaner has warned that anti-Semitism is "spreading like poison" in the country.
Statistics published last week showed a rise of 74% in the number of anti-Semitic attacks in France, from 311 in 2017 to 541 in 2018.
Several high-profile recent incidents have brought the issue of anti-Semitism into focus in France.
Post-boxes featuring a Holocaust survivor's portrait were daubed with swastikas, while a Jewish bakery in central Paris had the German word for Jews ("Juden") spray-painted on its window.
Last weekend, police also stepped in to protect the philosopher, Alain Finkielkraut, after he was reportedly bombarded with anti-Jewish taunts by a group of "yellow vest" protesters in Paris.
Jewish groups have also been warning that a rising far right across Europe has been promoting anti-Semitism and hatred of other minorities.
Crime data from Germany released last week revealed that anti-Semitic offences had increased by 10% over the past year - including a 60% rise in physical attacks.
Attacks have been blamed on both the far right and Islamists.