“Mr Ward’s comments are offensive and shocking, but more shocking still is the continued impunity that he seems to enjoy from his party.”
He added: “I was heartened to read of your promise to the Jewish community at your Chanucah reception only three weeks ago, to ‘speak out against the politics of vitriol, of blame, of grievance, of hatred’.
“I urge you to take forceful and immediate action to implement this commitment fully within the party you lead.”
Mr Ward has previously been condemned over his tweets about Jews and Israel.
The Bradford East MP previously said he would “probably” fire a rocket if he lived in Gaza.
In 2013, ahead of Holocaust Memorial Day, he accused “the Jews” of afflicting “atrocities on the Palestinians”.