The International Court of Justice in The Hague will hold hearings from January 11 to January 12 on a filing by South Africa that alleges "genocidal acts against the people in Gaza" and seeks to order Israel to end the military operation.
"This submission is meritless, counterproductive and completely without any basis in fact whatsoever," White House National Security Council spokesman John Kirby told a briefing.
State Department spokesman Matthew Miller said separately that from a U.S. assessment, "We have not at this point seen acts that constitute genocide."
"Genocide is, of course, a heinous atrocity," Miller told reporters. "Those are allegations that should not make be made lightly."
The court usually takes one or two weeks to issue a decision on emergency measures after the hearings. The court's rulings are final but it has no authority to enforce them.
Israel has angrily rejected the accusation by South Africa, with the foreign ministry calling it "blood libel," a reference to ancient antisemitic conspiracies.
FILE - South African President Cyril Ramaphosa addresses the 78th United Nations General Assembly at UN headquarters in New York City on September 19, 2023.
South Africa has often criticized Israel and alleged parallels to its own history of apartheid.
In The Hague application, South Africa says that Israel has been acting "with the requisite specific intent... to destroy Palestinians in Gaza as part of the broader Palestinian national, racial and ethnical group."
Palestinian Hamas militants infiltrated Israel on October 7 and killed some 1,140 people, mostly civilians, according to an AFP tally based on official Israeli figures.
In response to the deadliest attack in its history, Israel launched a relentless offensive that has reduced vast swathes of Gaza to rubble and claimed over 22,300 lives, according to the health ministry in the Hamas-run territory.
U.S. relations with South Africa have already been shaken over Pretoria's refusal to join Western pressure on Russia over its invasion of Ukraine.
The U.S. ambassador publicly accused South Africa last year of sending a ship of weapons to Russia, claims walked back by the State Department.
Some information in this report came from Agence France Press (AFP) and Reuters.