"Declarations of Intervention in support of South Africa's invocation of the Genocide Convention against Israel will increase the likelihood that a positive finding of the crime of genocide will be enforced by the United Nations," said the coalition.
Groups that have joined the call include Progressive International, World Beyond War, the Palestinian Assembly for Liberation (PAL, PEN International-Palestine, and the National Lawyers Guild.
"South Africa is correct in charging that under the Convention on the Prevention and Punishment of the Crime of Genocide, Israel's actions 'are genocidal in character, as they are committed with the requisite specific intent... to destroy Palestinians in Gaza as a part of the broader Palestinian national, racial, and ethnic group," the letter reads.
The letter was released days after South Africa filed its claim, asking the ICJ to declare that Israel has breached its obligations under the Genocide Convention, to which it is a party.
The death toll in Gaza has reached at least 22,313, with at least 57,296 people wounded and thousands feared dead under rubble. Since Hamas' attack on southern Israel on October 7, with support from the U.S., Israel has bombed hospitals, refugee camps, and residential buildings, all while claiming it is taking steps to protect civilian lives and targeting Hamas.
High-level Israeli government officials have also made numerous statements explicitly calling to wipe out Gaza's 2.3 million residents, either through warfare or by forcibly displacing them.
South Africa detailed several of the statements in its 84-page complaint, including President Isaac Herzog's claim that the entire population of Gaza, including roughly 1 million children, are "responsible" for Hamas' attack and are therefore legitimate military targets; Minister of Defense Yoav Gallant's statement that he had "released all restraints" on the military to fight Gaza's "human animals"; Energy Minister Israel Katz's demand that "all the civilian population in Gaza is ordered to leave immediately"; and Deputy Speaker of the Knesset Nissim Vaturi saying, "Now we all have one common goal—erasing the Gaza Strip from the face of the Earth."
"Finding evidence to establish intent is normally the obstacle to classifying genocide," saidGuardian columnist Owen Jones of South Africa's documentation on Tuesday. "You read through the endless statements and are left with no doubts on intent."
Suzanne Adely, president of the National Lawyers Guild, said that "the increasing global isolation of Israel and the U.S. and their European allies is an indicator that this is a key moment for popular movements to move their governments in the direction of taking these steps and being on the right side of history."
The U.S. alone vetoed a resolution calling for a cease-fire in Gaza at the United Nations Security Council last month, and was joined by just nine other countries in voting against a cease-fire at the U.N. General Assembly, while 153 countries supported the resolution.
"It's imperative that more states follow South Africa's historic leadership demanding Israel is held accountable under international law," said Adely. "One clear and immediate way to do that is to file Declarations of Intervention supporting South Africa's filing."
The letter was released days after Haaretz reported that Israeli officials have been warned by legal advisers that a ruling in favor of an injunction against Israel is possible at the ICJ.
On Democracy Now! on Tuesday, international law expert Francis Boyle, who has successfully argued cases before the ICJ, said South Africa has a strong chance of winning its case.
"Based on my careful review of all the documents so far submitted by the Republic of South Africa, I believe South Africa will win an order against Israel to cease and desist from committing all acts of genocide against the Palestinians," said Boyle. "And under Article I of the Genocide Convention, all contracting parties, 153 states, will then be obliged, quote, 'to prevent,' unquote, the genocide by Israel against the Palestinians."
Boyle noted that former U.S. State Department official Joan Donoghue is the president of the ICJ, and will likely use her authority "to shape the proceedings in favor of Israel."
"However, I have also been advised that the Republic of South Africa is, as of now, nominating a judge ad hoc," Boyle said. "That is their right under the statute of the International Court of Justice. I don't have a name yet, but I would hope the South African judge ad hoc will do his or her best to try to keep Donoghue straight."
Collective pressure from other countries, said Palestinian attorney Lamis Deek, could be "a sharp turning point for Palestine" at the ICJ.
"Through the ICJ, South Africa is poised to strike a decisive blow against this brutal genocide and torture campaign led by Israel in coordination with the United States," said Deek, whose firm convened PAL's Commission on War Crimes, Justice, Reparations, and Return. "We need more states to file supporting interventions—and we need the court to feel the watchful eye of the masses so as to withstand what will be extreme U.S. political pressure on the court."
"International humanitarian laws and institutions are meant to be, and must be seen as, tools for the people, not distant abstractions," he added. "People can—and should—play a strategic and powerful role by integrating this advocacy into their solidarity work, not only until their governments file supporting interventions but until the ICJ delivers justice."