Melbourne’s tightly-knit Orthodox community is reeling following the public ostracism of a group of dissident Lubavitchers accused of “a massive and reckless” act of blasphemy.

A video posted last week on YouTube shows the group celebrating a seudah, or religious feast, on the Fast of Tevet on December 27, when Orthodox Jews are supposed to mourn the day the First Temple was besieged.

The group, led by Alex Leonard and Asher Rozenfeld, appeared to include about 25 men, women and children singing, dancing, waving the yellow Chabad messianist flag and saying special prayers celebrating the Lubavitcher Rebbe, Menachem Mendel Schneerson — who died in 1994 — as the Messiah.According to Jewish tradition, fasts are replaced by feasts in the messianic era.

But their actions prompted a severe rebuke from Rabbi Zvi Telsner, chief rabbi of Melbourne’s Chabad community. Rabbi Telsner, a former rabbi at Finchley Central Synagogue, issued a scathing statement on Sunday against the “perpetrators of such misguided deeds”, saying that the fact they publicised their “transgression” on the web “constitutes a massive and reckless Chillul Hashem”, or desecration of God’s name.

In his ruling, plastered on the walls of the Yeshiva Centre, Lubavitch’s local headquarters, he said the dissidents cannot be counted as part of a minyan, are not allowed to answer “amen” in shul, cannot receive an aliyah to the Torah and no members of the community should speak to or have any business dealings with them until they seek forgiveness before a Jewish court.

But Mr Rozenfeld and Mr Leonard, who were reportedly expelled from the Yeshiva Centre several years ago, said they had not seen the edict.

“We are free to talk to anybody we choose and to carry on our business as usual,” Mr Rozenfeld said. Stating that he suspected the edict — which does not list names — constituted “character defamation”, he added: “I find it strange that a letter of such serious content would be issued publicly without me or anyone in the video receiving it first.”

Rabbi Telsner — who in 2004 himself signed a letter declaring the Rebbe is the Messiah — hosed down suggestions he had ordered an excommunication.

“It’s a statement about people who have transgressed. Their behaviour was in total disregard of Jewish law.”

While some Orthodox Jews in Melbourne are bemused, others believe it raises serious questions about Chabad, which split after the Rebbe’s death between those who believed he was the Messiah and those who did not.

Yossi Aron, the religious affairs editor of the Australian Jewish News, said: “This is much, much bigger than just a story about a few Orthodox rebels in Melbourne. This raises the question of messianism and Chabad. It now has to take a long hard look at itself.”

Ephraim Finch, executive director of the Melbourne Chevra Kadisha, added: “It would have been great if the Rebbe was Moshiach. He was a great person but he was not Moshiach. He died.”

Another Lubavitcher, Raphael Aron, said the furore “questions the ability of Chabad to continue without a Rebbe.

“It raises existential questions about the future of Chabad. Is the Rebbe Moshiach? Is there another Rebbe or are we waiting until Moshiach? It’s a discussion no one is prepared to have.”

An expert on cults, Mr Aron said the dissident group is “behaving in a cultish manner. It’s like they’re in some sort of trance.”

The maelstrom has spawned hundreds of comments on Jewish websites. “Every Lubavitcher needs to do some major introspection, and realise that they are at fault for this horrible Chillul Hashem,” wrote one contributor on theyeshivaworld.com. “It started out by believing in their hearts that the Rebbe was Moshiach, but denying it publicly. Then they crowned him Moshiach after his stroke. When he went into a coma they stated he could not die because he’s Moshiach. Finally when he died they started to come out with foolishness of a second coming. From there it’s just gone downhill.”