Arsonists have attempted to burn down a synagogue, while a rabbi in Frankfurt has received death threats, as the wave of anti-Semitic attacks triggered by the conflict in Gaza continues in Germany.

At 2.15 Tuesday morning a resident of the western city of Wuppertal near Dusseldorf rang the police after seeing flames in the street in front of the Bergische Synagogue.

The synagogue, which was first built in 1897, was burned to the ground during the Nazi Kristallnacht pogrom in 1938 and then rebuilt.

Police said they believed three young men had thrown six molotov cocktails at the doors. One 18-year old suspect, said to be in possession of a residence permit but whose nationality was unknown, was arrested. No one was injured and the synagogue was only slightly damaged, according to the Westdeutsche Allgemeine Zeitung.

Interior minister for North Rhine-Westphalia Ralf Jäger called the attack “cowardly and underhanded. Violence and anti-Semitism cannot be justified by anything.”

Meanwhile in Frankfurt am Main, a rabbi received a telephone call from a man threatening to kill 30 Jews in the city if his family in Gaza were harmed.

Dieter Graumann, president of the Central Council of Jews in Germany told the Frankfurter Rundschau on Tuesday that the rabbi received the call last Friday from a Palestinian man. Graumann said the Jewish community was taking the threat seriously, according to The Local.

Both incidents happened against a background of increasing anti-Semitism in Germany.

RT.com reports on a research project into anti-Semitism led by Monika Schwarz-Friesel, at Berlin’s Technical University.

According to Schwarz-Friesel there has been a huge increase in anti-Jewish sentiment online. Many of the insults were “falling back on old stereotypes,” with people using phrases like “usurer,” “child murderer” and “global conspiracy.”

“The Internet has become the primary distribution medium for the new anti-Semitism,” the Technical University said in a statement Monday.