Protesters waving Palestinian flags and signs of late leader Yasser Arafat have in recent days shouted anti-Semitic slogans at rallies against Israel's Gaza offensive, according to German media.
Exclaiming "Allahu Akbar" (God is great), crowds in Berlin have reportedly yelled "Death to Israel" and chanted "Zionists are fascists, killing children and civilians".
A Berlin imam has openly called for the annihilation of Zionist Jews, asking Allah to "kill them to the very last one," according to a video published online by Israel's Haaretz daily.
"We would never in our lives have thought it possible anymore that anti-Semitic views of the nastiest and most primitive kind can be chanted on German streets," he said in a statement.
He demanded "clear and loud condemnations from politicians, the media and civil society" against the hatred in the country that perpetrated the Holocaust.
"Jews are once again openly threatened in Germany and sometimes attacked, synagogues are being defaced and declared as targets," he said.
The centre-left Social Democrats party in a statement agreed, declaring: "Anti-Semitism, in whatever form, is in no way acceptable. Whoever supports or propagates is not in their right mind."
Berlin police, meanwhile, told Berlin daily Tagesspiegel that officers would from now take action if protesters repeat certain phrases from past rallies, including "Jew, Jew, cowardly pig, come out and fight alone".
The American Jewish Committee meanwhile demanded that German prosecutors investigate the reported statements of the imam, identified by the committee as Bilal Ismail, in the sermon delivered last Thursday.