The Palestine Solidarity Campaign has told supporters posting anti-Semitic messages on its Facebook page that they are “not welcome,” after an investigation showed thousands of hateful posts.

The group took action this weekend to remove offensive messages including Jewish conspiracy myths, Holocaust denial and Holocaust revisionism from its Facebook page, which has almost 500,000 likes.

A statement on the organisation’s website read: “PSC has been made aware of a number of unacceptable posts made by members of the public on our Facebook wall. These are abhorrent.”

It said the PSC was fundamentally opposed to racism of all kinds, including anti-Semitism and Islamophobia, adding: “Those who do not share those values are not welcome.”

Among the comments highlighted on the group’s Facebook page were phrases such as “filthy Jew dirt-bags” and others describing Jews as “the cancer of the world”.

It followed an investigation by the Campaign Against Antisemitism (CAA) Online Monitoring Unit, which reviewed nearly 3,000 comments and categorised them according to the international definition of anti-Semitism now used by the British government and the College of Policing.

“PSC’s Facebook presence is a cesspool of anti-Semitism which proliferates and normalises hatred of Jews,” said Gideon Falter, CAA chairman.

“We challenge the patrons, trade unions and students’ unions that endorse PSC to act on their commitment to fight racism by ending their association with PSC until it unequivocally endorses and enforces the international definition of anti-Semitism used by the British Government.”