Israel will fight South Africa's claim that it is committing "genocidal" acts in Gaza at the International Court of Justice, an Israeli spokesman has said.
"History will judge you, and it will judge you without mercy," Eylon Levy said, addressing South African leaders.
South Africa filed the case at the ICJ on Friday, to Israel's outrage.
South Africa is a staunch supporter of the Palestinians and has repeatedly condemned Israel since the start of the war with Gaza on 7 October.
More than 22,000 Palestinians - the majority of them civilians - have been killed in Israeli strikes since the war began, according to Gaza's health ministry which is run by the Islamist group Hamas.
Israel declared war on Hamas after the group led a massive attack on communities inside Israel, killing about 1,200 people, mostly civilians, and taking some 240 others back to Gaza as hostages.
Following its application to the ICJ, South Africa's presidency said that the country was obliged "to prevent genocide from occurring".
The 84-page document states that the "acts and omissions by Israel" are "genocidal in character because they are intended to bring about the destruction of a substantial part of the Palestinian national, racial and ethnical group".
South African government lawyers are preparing for the case to be heard on 11 and 12 January, Clayson Monyela, a spokesperson for South Africa's Department of International Relations and Cooperation, said on X.
The ICJ, which is based in the Hague in the Netherlands, is the UN's highest court. It settles disputes between states and gives advisory opinions on international legal issues. It does not have the power to bring prosecutions. However, its opinions carry weight with the UN and other international legal bodies.
Israeli intended to fight the case, Eylon Levy said, "to dispel South Africa's absurd blood libel".
A blood libel is a term used to describe antisemitic false allegations against Jewish communities of bloodletting, originating in Europe in the Middle Ages.
Israeli Prime Minister Benjamin Netanyahu angrily rejected South Africa's allegations when it filed the lawsuit, saying "No, South Africa, it is not we who have come to perpetrate genocide, it is Hamas.
"It would murder all of us if it could. In contrast, the IDF [Israeli army] is acting as morally as possible."
It comes as Israel is already facing an investigation by the ICJ, initiated by the Palestinians, into its "prolonged occupation, settlement and annexation of... Palestinian territory".
The court has sat in judgement on Israel once before, in 2004, when it found that Israel's barrier built in and around the occupied West Bank was against international law. Israel said the barrier was built to thwart suicide bombings from the West Bank; Palestinians considered it a mechanism to take land.
