(AFP) - South Africa on Thursday accused Israel of breaching the UN Genocide Convention, saying that even the deadly October 7 Hamas attack could not justify such alleged actions, as it opened a case at the top UN court.

Pretoria has lodged an urgent appeal to the International Court of Justice (ICJ) to force Israel to "immediately suspend" its military operations in Gaza.

Israel has dismissed the case as "atrocious" and "preposterous" and will lay out its own defence on Friday.

"No armed attack on a state territory no matter how serious... can provide justification for or defend breaches of the convention," said Pretoria's Justice Minister Ronald Lamola.

"Israel's response to the October 7 attack has crossed this line and given rise to the breaches of the convention," he added.

- 'Genocidal acts' -

The war in Gaza erupted when Hamas launched its unprecedented attack, which resulted in about 1,140 people killed in Israel, mostly civilians, according to an AFP tally based on official figures.

Israel has responded with a relentless military campaign that has killed at least 23,357 people, mostly women and children, according to Gaza's Hamas-run health ministry.

A world away from the death and destruction in Gaza and Israel, robed lawyers battled it out with technical legal arguments in the Peace Palace in The Hague.

South Africa argues Israel is breaking its commitments under the UN Genocide Convention, a treaty signed in 1948 in the wake of the Holocaust.

Top lawyer for South Africa Adila Hassim said Israel's bombing campaign aimed at the "destruction of Palestinian life" and had pushed Palestinians "to the brink of famine".

"Genocides are never declared in advance, but this court has the benefit of the past 13 weeks of evidence that shows incontrovertibly a pattern of conduct and related intention that justifies a plausible claim of genocidal acts," she said.

As a fellow signatory to the treaty, South Africa can take Israel to the ICJ, which rules on disputes between countries and is often described as the "World Court".

The ruling African National Congress (ANC) has long been a firm supporter of the Palestinian cause, often linking it to its own struggle against the white-minority government, which had cooperative relations with Israel.

South Africa has acknowledged the "particular weight of responsibility" of accusing Israel of genocide. It "unequivocally" condemned the Hamas attacks that touched off the war in Gaza.

- 'Brazen gall' -

Israel President Isaac Herzog has already hinted at his country's likely defence against what he called an "atrocious and preposterous... claim".

"We will present proudly our case of using self defence... under international humanitarian law," he said.

Prime Minister Benjamin Netanyahu slammed South Africa in a statement, saying it was Israel that was fighting "genocide" committed by Hamas militants.

"The State of Israel is accused of genocide at a time when it is fighting genocide," Netanyahu said in the wake of South Africa's submission.

"A terrorist organisation carried out the worst crime against the Jewish people since the Holocaust, and now someone comes to defend it in the name of the Holocaust? What brazen gall. The world is upside down," he said.

The United States too is backing its ally Israel, with the State Department describing the charges as "unfounded".

But Washington also distanced itself from some of the Israeli criticism of South Africa.

Asked about Israel's charge that South Africa was serving as Hamas' "legal arm," State Department spokesman Vedant Patel told reporters that "that is not a characterisation I would make from up here when it comes to our South African partners."

"But again, we continue to feel very strongly that the allegations that Israel is committing genocide are unfounded," Patel said.

As it is an urgent procedure, the ICJ could rule in a matter of weeks.

Its rulings are final and cannot be appealed. However, countries do not always follow the court's verdicts -- the ICJ has ordered Russia to stop its invasion of Ukraine, for example.

But a court ruling against Israel would certainly increase political pressure on the country, with many speculating it could serve as a pretext for sanctions.

Cecily Rose, assistant professor of public international law at Leiden University, noted the court did not have to rule on the fundamentals of the case at this stage -- that issue will likely take years.

"Instead, the court would only be evaluating whether there is a risk of irreparable prejudice to rights held under the Genocide Convention, in particular the right of the Palestinians in Gaza to be protected from acts that threaten their existence as a group," Rose told AFP.

Dutch police kept rival demonstrations apart in The Hague. Hundreds of pro-Israeli protesters waving flags marched through the streets while a smaller group of pro-Palestinian supporters brandished placards saying: "End Israel apartheid."

© Agence France-Presse