Israeli police say vandals have scrawled graffiti and affixed a knife with a Biblical verse at the home of a leader of a group advocating secular Judaism.

Police say they are investigating Thursday's incident at the home of Yaakov Malkin, the provost of the International Institute for Secular Humanistic Judaism.

The institute's website defines Secular Humanistic Judaism as a "cultural Jewish identity" with a "human-focused non-theistic philosophy of life."

Rabbi Sivan Maas, Malkin's daughter, says vandals sprayed graffiti citing a verse from Psalms that says "Do I not hate those who hate you, Lord." An anonymous letter addressed to Malkin threatened him if he did not stop advocating "atheism."

Maas denied the institute promotes atheism.

Suspected Jewish extremists have targeted advocates of non-Orthodox Judaism over the past years.