GAZA CITY, Gaza Strip — United Nations officials charged Israel had violated international law after artillery shells slammed into a school overflowing with evacuees on Wednesday.
It was one of the worst mass-casualty incidents of the three-week war. The building was the sixth U.N. school in the Gaza Strip to be rocked by explosions during the conflict.
Israeli officials said they were trying to determine who was responsible for the bloodshed. In past incidents the Israeli military blamed errant rocket or mortar fire by Gaza militants for explosions at U.N. schools — or said the blasts were under investigation.
The U.N. Relief and Works Agency (UNRWA), which operated the school-turned-shelter, said it had gathered evidence, analyzed bomb fragments and examined craters after the attack. Its initial assessment was that three Israeli artillery shells hit the school.
"I condemn in the strongest possible terms this serious violation of international law by Israeli forces," UNRWA Commissioner-General Pierre Krahenbuhl said. "This is an affront to all of us, a source of universal shame. Today the world stands disgraced."
U.N. Secretary-General Ban ki-Moon said "all available evidence points to Israeli artillery as the cause" of the predawn attack.
The White House issued a statement condemning the attack on the school and lamenting the deaths, but did not mention Israel as the possible source of the fire.
A spokesman for the Israeli military, Lt. Col. Peter Lerner, called the shelling of the school "a true tragedy," and said the incident was under investigation.