The source of a deadly attack on a United Nations-run school in Gaza on Thursday remain unclear, with the Palestinians blaming Israel for the deaths, and the Israeli army saying it does not know whether Israeli shelling or a Hamas rocket hit the facility, killing a reported 15 people.

The Israeli army says the army fired mortars in the area of the UNRWA school in Gaza after Israeli troops were shot at from the area of the school. Palestinian sources said 15 people were killed when the school in Beit Hanoun was hit Thursday afternoon.

However, army spokesperson Moti Almoz told Israel's Channel 2 on Thursday evening that the military does not know whether it was Israel Defense Forces fire that hit the school. An IDF source said that army representatives made contact with UNRWA and the Red Cross over the past few days to inform them that troops were shot at from near the school, and that the IDF would return fire toward the source of the shooting, which was located near the school.

The IDF stated that Hamas rockets had landed in the Beit Hanoun area during fighting with its forces, and that those rockets may be responsible for the deaths.

The IDF Spokesman later issued a statement that it is investigating the matter of the hit on the school. Terrorists opened fire at IDF personnel from the area of the school, according to the spokesman, and soldiers returned fire toward the source of the shooting. Likewise, stated the spokesman, Hamas fired at the school, and despite repeated warnings and appeals to international authorities to remove civilians from these areas of fighting, they were not evacuated.

UN Secretary-General Ban Ki-moon condemned the attack on the UNRWA school for Palestinian refugees in northern Gaza. Ban demanded that Israel and Hamas abide by international humanitarian law during their conflict and respect "the sanctity of civilian life, the inviolability of UN premises" and protect humanitarian workers.

He said in a statement in Erbil, Iraq, which was released at UN headquarters, that the "circumstances are still unclear." Ban said UN staff members were attempting to arrange "a humanitarian pause in the hostilities so that civilians could be evacuated."

"Today's attack underscores the imperative for the killing to stop — and to stop now," Ban said.