U.N. Secretary-General Ban Ki-moon has called the Israeli attacks on U.N. facilities in Gaza "totally unacceptable.”

In a statement issued Tuesday after the Israeli attacks on three U.N. schools in Gaza, Ban said “the attacks by Israeli military forces which endanger facilities acting as places of refuge are totally unacceptable and must not be repeated."

He added that any actions by militants which endanger the Palestinian civilian population are equally unacceptable.

Currently, some 15-thousand Palestinians are estimated to be taking refuge in 23 U.N. schools in Gaza. The U.N. has regularly given the Israeli army exact geographical coordinates of its facilities to try to keep them safe from attack.