FRANKFURT - Armed guards have been posted at synagogues throughout Germany for the start of Yom Kippur, the Day of Atonement. Anti-Semitism is once again on the rise in Europe, especially in Germany.

The tensions have been building in Germany since demonstrations against last summer's Gaza war exposed a clear anti-Jewish sentiment. Chants were heard that echoed from Germany's darkest times.

"Jew, Jew! Cowardly pig," they said.

"We haven't had this dimension at all before," said Deiter Graumann, president of the Central Council of Jews in Germany. "When you imagine in German streets, people here chanting - a roaring mob chanting - Jews to be gassed, to be slaughtered, to be burned."

He said he doesn't quite believe the sentiments have spiked because of passions that were stirred up by the events in Gaza.

"It is cited as a reason for that but I don't think it's a reason," Graumann said. "It's a pretext. It's an occasion to let it out."

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Much more of the incendiary street rhetoric has come from German Muslims, many of whom are recent immigrants.

But Monika Schwartz Friesel, of Berlin's Technical University, has studied thousands of anti-Semitic emails sent to German-Jewish institutions and made a disturbing discovery.

"We saw that more than 60 percent of the writers, who clearly evoke anti-Semitic stereotypes, come from the middle of society and many of them are highly educated," she said.

The memories of Jewish persecution -- of the November 1938 Kristallnacht when Jewish institutions were destroyed -- are burned into German memory. Frankfurt's main synagogue, badly damaged that night, is one of those now under armed guard.

Anti-Israeli protests that become anti-Semitic demonstrations may be taking place across Europe, but nowhere are the echoes more sinister than they are here in Germany. This may not be 1938, but once again the Jewish community here says it feels like it's under siege.

"They are worried," said Graumann. "And many Jews here ask the question 'Has our Jewish population a future in Germany?' I haven't heard that question for many, many years."

Now, though, the question is being asked again.