Secretary-General Ban Ki-moon is condemning a deadly attack on a UN school for Palestinian refugees in northern Gaza that killed many Palestinians who sought refuge there from Israeli shelling as well as UN staff.

The UN chief again 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 are 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.