The president of J Street, one of the largest pro-Israel advocacy groups in the United States, has acknowledged that Israel has broken the international genocide convention in its carnage in Gaza.

"I have ... been persuaded rationally by legal and scholarly arguments that international courts will one day find that Israel has broken the international genocide convention," Jeremy Ben-Ami wrote in a blog post published Sunday.

Ben-Ami described the realisation as deeply personal and painful, asking: "How can it be that Israel – the state founded by a people who experienced genocide – could itself be committing this most heinous of crimes?"

He noted that for many in the Jewish community, the idea is "inconceivable," and even raising the question is seen as an "outrage."

The longtime pro-Israel figure cited Israel’s denial of food and basic necessities to civilians, soldiers shooting at people trying to collect aid, the destruction of Gaza’s entire infrastructure, and the forced displacement of the population into "intolerably small areas" as violations that "simply have no justification."

"Until now, I have tried to deflect and defend when challenged to call this genocide," Ben-Ami admitted.

"I cannot and will not argue any more against those using the term. I simply won't defend the indefensible."

He said his past hesitation stemmed from his family's history and a reluctance to equate Israel with genocidal regimes, but added that facts on the ground had changed his position.

Ben-Ami predicted that Prime Minister Benjamin Netanyahu and others in the Israeli government will one day be held accountable in court, though those proceedings will be "deemed antisemitic" by some Jewish organisations.

"This government and these leaders will be remembered with revulsion for the horrors they’ve overseen," he wrote.