More than 800 serving officials in the US and Europe have signed a statement warning that their own governments' policies on the Israel-Gaza war could amount to "grave violations of international law".

The "transatlantic statement", a copy of which was passed to the BBC, says their administrations risk being complicit in "one of the worst human catastrophes of this century" but that their expert advice has been sidelined.

It is the latest sign of significant levels of dissent within the governments of some of Israel's key Western allies.

One signatory to the statement, a US government official with more than 25 years' national security experience, told the BBC of the "continued dismissal" of their concerns.

"The voices of those who understand the region and the dynamics were not listened to," said the official.

"What's really different here is we're not failing to prevent something, we're actively complicit. That is fundamentally different from any other situation I can recall," added the official, who spoke on condition of anonymity.

The statement is signed by civil servants from the US, the EU and 11 European countries including the UK, France and Germany.

It says Israel has shown "no boundaries" in its military operations in Gaza, "which has resulted in tens of thousands of preventable civilian deaths; and… the deliberate blocking of aid… putting thousands of civilians at risk of starvation and slow death."

"There is a plausible risk that our governments' policies are contributing to grave violations of international law, war crimes and even ethnic cleansing or genocide," it said.

The identities of those who signed or endorsed the statement have not been made public and the BBC has not seen a list of names, but understands that nearly half are officials who each have at least a decade of experience in government.

One retired US ambassador told the BBC that the coordination by dissenting civil servants in multiple governments was unprecedented.

"It's unique in my experience watching foreign policy in the last 40 years," said Robert Ford, a former American ambassador to Algeria and Syria.

"[Then there were] people who knew better, who knew that intelligence was being cherry-picked, who knew that there wasn't a plan for the day after, but nobody said anything publicly. And that turned out to be a serious problem," he said.

"The problems with the Gaza war are so serious and the implications are so serious that they feel compelled to go public," he said.

The officials argue the current nature of their governments' military, political or diplomatic support for Israel "without real conditions or accountability" not only risks further Palestinian deaths, but also endangers the lives of hostages held by Hamas, as well as Israel's own security and regional stability.

"Israel's military operations have disregarded all important counterterrorism expertise gained since 9/11… the [military] operation has not contributed to Israel's goal of defeating Hamas and has instead strengthened the appeal of Hamas, Hezbollah and other negative actors".

The officials say they have expressed their professional concerns internally but have been "overruled by political and ideological considerations".

One senior British official who has endorsed the statement told the BBC of "growing disquiet" among civil servants.

The official referred to the fallout from last week's preliminary ruling by the UN's International Court of Justice in a case brought by South Africa which required Israel to do all it can to prevent acts of genocide.

"The dismissal of South Africa's case as 'unhelpful' by our Foreign Secretary puts [the international rules-based] order in peril."

"We have heard ministers dismiss allegations against the Israeli Government seemingly without having received proper and well-evidenced legal advice. Our current approach does not appear to be in the best interests of the UK, the region or the global order," said the official who also spoke on condition of anonymity.

The US State Department, the European Union Commission and the UK Foreign, Commonwealth and Development Office have been approached for comment.

The statement suggests that while Israel's military operation has caused unprecedented destruction of lives and property in Gaza, there appears to be no workable strategy to effectively remove Hamas as a threat, nor for a political solution to ensure Israel's security in the longer term.

It calls for the US and European governments to "stop asserting to the public that there is a strategic and defensible rationale behind the Israeli operation".

Israeli officials have consistently rejected such criticism. In response to the new statement, the Israeli embassy in London said it was bound by international law.

It added: "Israel continues to act against a genocidal terrorist organisation which commits war crimes as well as crimes against humanity."

Prime Minister Benjamin Netanyahu has claimed that only full military pressure on Hamas will secure the further release of hostages, while the army says it has destroyed significant underground infrastructure used by the group, including command centres, weapons sites and facilities for holding hostages.

On Saturday, the Israeli military said: "Throughout [the city of] Khan Yunis, we have eliminated over 2,000 terrorists above and below ground."

Israel has repeatedly rejected claims it deliberately targets civilians, accusing Hamas of hiding in and around civilian infrastructure.

Since the start of the war, more than 26,750 Palestinians have been killed and at least 65,000 injured, according to health officials in the Gaza Strip, which has been governed by Hamas and blockaded by Israel and Egypt since 2007.

Israeli officials say that 9,000 of those killed were Hamas militants but have not provided evidence for the figure. More than 1,200 people were killed in Israel during the Hamas attacks of October 7th, and a further 100 died of their injuries according to Israeli officials. More than 250 people were taken as hostages into Gaza.

The US administration has repeatedly said that "far too many Palestinians have been killed" in Gaza, and that Israel has the right to ensure October 7th "can never happen again".