European voters risk giving their countries a bad name by electing far-right politicians, the leader of the World Jewish Congress warned Saturday ahead of a major rally against anti-Semitism.

WJC president Ronald Lauder also voiced concern that Islamic extremists are trying to "use all means," particularly online, to stir hatred and pointed to the threat posed by radicalized Muslims returning from Syria and Iraq.

Chancellor Angela Merkel and Lauder are to speak at Sunday's rally in Berlin, organized after tensions over the Gaza conflict spilled over into demonstrations in Europe that saw anti-Jewish slogans and violence. In May, European Parliament elections brought successes for far-right parties, particularly in France.

"One person representing a country who is extreme will give their whole country a bad name," Lauder told The Associated Press. "When people vote who goes to the parliament they have to say to themselves, 'who do we really want to represent us, who do we really want to be the face of what people see of our country?'"

Lauder said that, while only a small percentage of Muslims in Europe took part in recent demonstrations, "what worries me very, very much are the political agitators on the part of the Muslim extremists who are trying to use all means, particularly through the Internet, to get people angry."

European countries are worried about the return of citizens who fought with the Islamic State group or others who might commit attacks at home. Lauder said that "this is the major threat."

Officials say at least 400 people from Germany have gone to Syria and Iraq to fight with extremist groups.

The government Friday banned all activity on behalf of Islamic State, including the distribution of propaganda. "It should have been taken off the air sooner," Lauder said.