AP - The White House says there is little doubt Israeli artillery hit a United Nations school in Gaza and is describing the shelling as "totally unacceptable and totally indefensible."

White House spokesman Josh Earnest cited statements from the UN blaming Israel for the shelling, as well as the Israeli government's acknowledgement that it was firing in the area of the school. Earnest says that while the U.S. supports a full investigation into the matter, "it does not appear there's a lot of doubt about whose artillery was involved."

In its initial statements after the shelling, the White House condemned the attack but specifically did not assign responsibility.

Earnest reiterated that Israel can do more to ensure the safety of civilians in the clashes between Israel and Hamas.

While the U.S. says it supports Israel's right to defend itself against Hamas, officials have repeatedly called on Israel to do more to stem civilian casualties. More than 1,300 Palestinians, mostly civilians, and more than 50 Israelis, almost all of them soldiers, have been killed since July 8.

The White House continues to call for an immediate humanitarian cease-fire but there appeared to be little sign that one was imminent. Israeli Prime Minister Benjamin Netanyahu said Thursday that Israel will destroy the Hamas tunnel network in the Gaza Strip "with or without a cease-fire," as the military called up another 16,000 reservists to pursue its campaign in the densely-populated territory.