The Israeli military said Hamas "terror operatives" were among the dozens of dead at a UN-run school hit by tank shells in the Gaza Strip and that mortar fire had come from the building.
The Israeli strike near Al-Fakhura school in Jabaliya in northern Gaza killed 43 people, according to Gaza medical services, and has been condemned by the United Nations and governments worldwide.
An Israeli military spokesman said on Tuesday, "it has been found that among the dead at the Jabaliya school were Hamas terror operatives and a mortar battery cell who were firing on IDF (Israeli military) forces in the area."
The dead Hamas militants found at the scene were named as Imad Abu Askhar and Hassan Abu Askhar.
"We face a very delicate situation where the Hamas is using the citizens of Gaza as a protective vest," military spokesman Brigadier General Avi Benayahu said.
The strike was one of three on UN-run schools in Gaza yesterday.
UN chief Ban Ki-moon said he was "deeply dismayed" by the Israeli military attacks and called them "totally unacceptable."
The Israeli military said in a briefing that preliminary investigations indicate that Hamas fired mortar bombs from the area of the school towards Israeli forces, who returned fire at the source of the shooting.
"The Israeli return fire landed outside the school, yet a series of explosions followed, indicating the probable presence of munitions and explosives in the building," the military official said in the briefing.