At least 16 people were killed and more than 200 injured Thursday when a school used as a United Nations shelter came under fire in Gaza. Palestinian families displaced by the assault had reportedly gathered to move to a safer area when the school was hit. Palestinian officials have blamed Israeli tank shelling, while Israel has suggested militant rockets were at fault. The United Nations Relief and Works Agency for Palestine Refugees (UNRWA) has declined to directly accuse Israel, but says it gave the school’s coordinates to the Israeli army numerous times. "Within Gaza, there is no safe place," says Christopher Gunness, UNRWA spokesperson. "If the parties to this conflict have shown themselves callous enough to be able to hit a clearly designated, clearly marked U.N. compound where hundreds of people have come to take sanctuary, we cannot guarantee anymore the safety of our installations." Gunness says the number of people now seeking shelter amidst the violence has swelled to 150,000.