Facebook has refused to remove pages where internet users espouse Holocaust denial despite a plea from a group of Holocaust survivors.

Earlier this month 21 survivors of Nazi persecution signed a letter which was sent to Facebook, asking that Holocaust denial no longer be allowed as part of facebook's "free speech" policy.

The signatories described pages where users openly questioned what the Nazis did as "shameless, cynical and hateful propaganda".

The letter said: "As individuals who are both victims of and witnesses to the truth of the horrors and hate of that time period, we are deeply hurt and offended by your policy that protects Holocaust denial as speech.

"Above all else, Holocaust denial, in any form, is a desecration of our suffering the suffering and martyrdom of our murdered parents, brothers and sisters."

They said allowing such hate-propaganda on the social networking site enabled Holocaust deniers to preach their inherent message of lies and hate and called on Facebook "to live up to its moral and social responsibilities".

They said that if Facebook – founded by Jewish Harvard student Mark Zuckerberg in 2004 - did not take action, it would be "exposing the public and, in particular, youth to the antisemitism which fueled the Holocaust.

"Please correct this terrible error in judgment before our generation passes away."

However Facebook, who have previously been reluctant to challenge anti-Israel pages on the site, said they would not fulfil the request.

"We think it's important to maintain consistency in our policies, which don't generally prohibit people from making statements about historical events," said a Facebook spokesman. "No matter how ignorant the statement or how awful the event."

A spokesman for Facebook told MSNBC that they found the groups "repugnant and ignorant". But Andrew Noyes added: "The mere statement of denying the Holocaust is not a violation of our terms.

"However, if the members of the Holocaust denial groups consistently post hateful or threatening comments, we will take the groups down."

Mark Gardner of the Community Security Trust criticised the decision. "Social media sites treat freedom of speech as a get out of jail card, freeing them of any need for editorial control," he said.

"Facebook's behaviour here is deeply immoral and callous."

Rabbi Abraham Cooper of the Simon Wiesenthal Centre, said: "As the most powerful portal in social media it should show solidarity with the survivors of the Shoah.

"Failure to do so will not only cause needless anguish to to the survivors but inspire other hate propagandists to promote their agenda on Facebook's powerful platform."

He added: "Facebook has a full team poised to remove such pages. It is time the company that generally strives to do the right thing, does right by the victims of the Shoah."