Israel's deputy foreign minister has said the strike on a UN school in Gaza could have been the result of an errant rocket fired by Palestinian militants.
The strike is reported to have killed 15 people in the town of Beit Hanoun, although it has yet to be established who was responsible.
The UN Relief and Works Agency has called for an "immediate investigation" into the incident.
Tzachi Hanegbi told Radio 4's Today programme: "I don't know who caused this mistake.
"Some say it was an Israeli mistake, maybe it was a Palestinian mistake, because as you know every six rockets that Hamas is shooting at us falls in Gaza unfortunately for them."