"We are deeply concerned about reports of civilian casualties in Gaza" following the strike, National Security Council spokesman Sean Savett said in a statement.

"We are in touch with our Israeli counterparts, who have said they targeted senior Hamas officials, and we are asking for further details," Savett said.

Israel has insisted that it was targeting Hamas militants inside the religious school housing displaced Palestinians, but the attack has sparked international condemnation.

AFP could not independently verify the toll which, if confirmed, would be one of the largest from a single strike during 10 months of war between Israel and Palestinian militants since Hamas's October 7 attack.

Savett said Hamas has been using schools to operate out of, "but we have also said repeatedly and consistently that Israel must take measures to minimize civilian harm."

With authorities in Gaza saying that the death toll has topped 39,790 in the war, Savett said that "far too many civilians continue to be killed and wounded."

The strike "underscores the urgency of a ceasefire and hostage deal, which we continue to work tirelessly to achieve," he concluded.