Organisers of a pro-Israel conference say they are “shocked by the foul antisemitic abuse” people were leaving on their Facebook page.
The We Believe in Israel conference is due to take place in central London on March 22 and a post advertising the event online has been inundated with users leaving a “torrent of abuse”.
We Believe in Israel's director Luke Akehurst, said: “It actually shows exactly why we need a major conference like this to act as a springboard for a united pro-Israel fight back in the UK.”
Under a post promoting the event to Israel supporters, one user calling himself James Lisk wrote: “Holocaust. Biggest fabrication in history. And they get away with mass murder hiding behind the fact they are the persecuted Jews.
“What a complete load if s*** - the only reason they haven't been wiped out is because half of the American defence secretaries are Jewish. They can't hide the lies forever.
“And then I hope those accountable will be brought to justice.”
One post, left in the name of Saleem Ahmed, said: “Scum bags dogs, dirty filthy b*****ds , I pray you Zionists pigs burn as long as the hell fire burns.
“You are the worst of the worst. Every Palestinian you have killed , I pray to Allah you Zionists pigs never get forgiven.”
Another, posted in the name of Damien McAnoy, simply said “child killers” while, another said: “Nazis did well to protect themselves too against the Jews but shame they didn't go all the way.”
Mr Akehurst said the comments would be reported to Facebook.
The conference is expected to attract 1,500 delegates from across the political spectrum.
Organisers say it is aimed at people who support "the right of the state of Israel to live in peace and security".