UN Secretary-General Ban Ki-moon says the Israeli military was told 17 times that a UN school in Gaza was sheltering thousands of Palestinian families.
UN Secretary General Ban Ki-moon has condemned an Israeli strike on a Gaza school that killed 16 people as "unjustifiable," calling for those responsible to be held to account.
"This morning, a UN school sheltering thousands of Palestinian families suffered a reprehensible attack," Ban said during a visit to Costa Rica on Wednesday.
"It is unjustifiable, and demands accountability and justice."
The school in the Jabaliya refugee camp in northern Gaza, which was sheltering more than 3000 homeless people, came under attack from Israeli tank shells at dawn on Wednesday.
It is the second time in a week that a UN school housing refugees has been hit.
Ban accused the Israeli military of ignoring repeated communications on the location of the school.
"I want to make it clear that the exact location of this elementary school has been communicated to the Israeli military authorities 17 times, as recently as last night, just a few hours before this attack," he said.
"They are aware of the coordinates and exact location of where these people are."
Costa Rican President Luis Guillermo Solis, meanwhile, joined international calls for an end to the bloodshed.
"We want the immediate establishment of a UN-monitored ceasefire to enable an escape from this bloody vortex, which is an offence to humanity," he said.