Organisers of a pro-Israel conference say they are "shocked by the foul, antisemitic abuse" left on their Facebook page.
A post advertising the We Believe in Israel conference, which is due to take place in London on Sunday, has been the target for a "torrent" of hate, they said.
We Believe in Israel's director Luke Akehurst, said: "It 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."
One Facebook user calling himself James Lisk wrote on the post: "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 [sic] s--- - the only reason they haven't been wiped out is because half of the American defence secretaries are Jewish."
Another comment, left in the name of Saleem Ahmed, said: "Scum bags dogs, dirty filthy b------ds, I pray you Zionists [sic] 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".
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".