The World Jewish Congress (WJC), holding an emergency executive meeting two days after the stunning electoral success of the far-right in France, urged European governments to kill off anti-Semitism before it spread.
"To the political and intellectual leaders we send the following message -- we will never forget that once again you are standing by and doing nothing while synagogues burn in your cities," the Congress said in a statement.
It said media prejudice and pro-Palestinian statements by many politicians and prominent intellectuals had encouraged extremists in Europe to attack Jews and their property.
"The WJC notes with concern that European intellectual and political elites are creating an ambience in which anti-Semitism is considered legitimate," it said.
According to figures from the Congress, there have been 300 anti-Jewish attacks in the last three weeks, ranging from graffiti daubed on Jewish property to fire-bombings of synagogues and physical assaults on rabbis. Suspects in many of the attacks are Arab youths of North African origin.
In the most serious case, a synagogue in Marseille in the south of France was burned to the ground March 31.
In Belgium there have been a half dozen attacks on Jewish institutions, including the burning of a bookstore and a shooting at a synagogue.
There are Holocaust survivors who are telling their children: 'Look, this is exactly how it happened in the 1930s,"' when anti-Semitic attacks eventually led to genocidal slaughter of European Jews by Hitler's Nazi regime, WJC Secretary-general Avi Beker Beker said.
He said he still believed in the strong democratic institutions in Europe but added: "I'm quite disappointed I don't see the application."
French and Belgian leaders have already promised better protection for Jewish communities. It has done little to soothe worries, Beker said.
Beker said even some of the 100 delegates in Brussels were verbally abused on the streets and a Russian member was pushed around by a group of youths who stole his hat.
"This is really reminiscent of the worst times of Europe," he said. "It is part of an atmosphere. Not just a few hooligans."
The WJC said in would set up a European Jewish Information Center to monitor anti-Jewish attacks, suggest ways to prevent them and respond to media reports on the Middle East which it deems biased against Israel.
"We find Europe pretty sick. European Jewry is confronted with the strongest wave of anti-Semitic attacks since the end of World War Two," Serge Cwajgenbaum, secretary-general of the Paris-based European Jewish Congress, told Reuters.
Cwajgenbaum said far-right leader Jean-Marie Le Pen's surprise win through to the second round of the French presidential election showed that nationalism and anti-Semitism were on the rise in Western Europe.
"It reflects the malady which exists in different countries in Europe ... . We could never have expected even in our worst nightmares that Le Pen would succeed so much," he said.
The union of Jewish communities in France appealed Tuesday to Jewish voters to turn out en masse to vote against Le Pen, calling him a dangerous anti-Semite.
Israel's most powerful religious party, Shas, has urged French Jews to leave for Israel after Le Pen's strong performance.
Berlin police have given informal advice to Jewish people to avoid wearing skullcaps after recent anti-Semitic attacks in the German capital, a police spokesman said Tuesday.
Most significant Jewish sites in Berlin are guarded by armed police. Barricades surround buildings such as the historic New Synagogue.
The violence against Jews and Jewish property appears to be linked to protests against Israel's military incursions into Palestinian areas of the West Bank, although investigators have so far said it is the work of delinquents rather than an orchestrated campaign.
The World Jewish Congress reiterated its controversial view that anybody who is against Israel must automatically be anti-Semitic.
"It sees in the vilification and demonization of the Jewish state, anti-Semitism, plain and simple," the leaders said, voicing "unconditional solidarity" with Israel.
Five European governments appealed last week for joint EU action to combat racism after a spate of attacks on Jewish targets from Marseille to Kiev, but the EU and United Nations have also called on Israel to end its assault on the Palestinian territories.