Updated

Israel's military has acknowledged firing a mortar shell that hit the courtyard of a U.N. school in Gaza, but says the yard was empty at the time and that the shell could not have killed anyone.

Palestinian officials have said three Israeli tank shells hit the school in the town of Beit Hanoun last Thursday, killing 16 people and wounding scores. The school served as a shelter for Palestinians displaced by the Gaza fighting. At the time of the incident, witnesses said they were being urged to evacuate because of nearby clashes.

Lt. Col. Peter Lerner, an Israeli army spokesman, said Sunday that a military probe shows that "a single errant mortar landed," but that it is "extremely unlikely that anybody was killed as a result of this mortar."