(Adds details on conflict, White House comments)
By Phil Stewart
WASHINGTON, July 31 (Reuters) - The United States on Thursday called on Israel to do more to protect civilians in its military offensive in Gaza and condemned an Israeli strike on a U.N.-run school, even as it defended moves to resupply its close ally with ammunition.
The White House reiterated its position that it was Israel's right to defend itself and described the resupply of ammunition disclosed as the fighting raged this week as "routine."
White House spokesman Josh Earnest rejected suggestions that resupplying the Israelis might prolong the conflict, saying it was "part of a routine foreign military sales delivery."
"The requested items were readily available and were provided as they have been on numerous other occasions," Earnest said.
The U.S. officials spoke shortly before the United States and the United Nations jointly announced a 72-hour ceasefire and an agreement for Israeli and Palestinian delegations to meet in Cairo to seek a "durable ceasefire."
Gaza officials say more than 1,410 Palestinians, most of them civilians, have been killed in the enclave. Israel says 56 of its soldiers and three civilians have been killed.
Pentagon spokesman Colonel Steve Warren denounced the mounting death toll, saying: "The civilian casualties in Gaza have been too high."
"And it's become clear that the Israelis need to do more to live up to their very high standards - their very high and very public standards - for protecting civilian life," Warren said.
Earlier on Thursday, the top U.N. human rights official criticized the United States, Israel's main ally, for failing to sufficiently use its influence with Israel to halt the carnage.
The White House's Earnest used strong language to condemn the shelling of a U.N.-run school in Gaza. The United Nations said its initial assessment was that Israeli artillery shells hit the facility.
"The shelling of a U.N. facility that is housing innocent civilians who are fleeing violence is totally unacceptable and totally indefensible," Earnest said.
The Pentagon has said it allowed Israel to tap a U.S. stockpile inside Israel to restock two different types of ammunition.
It described the munitions on Thursday as 120 mm tank rounds and 40 mm illumination rounds, fired from grenade launchers. A U.S. defense official had offered a different description of the ammunition on Wednesday, saying they were grenades and mortar rounds.
The Pentagon said it was unclear if the munitions would be used for training or operations.
The munitions were part of a program managed by the U.S. military and called War Reserves Stock Allies-Israel (WRSA-I), which stores munitions locally for U.S. use that Israel can also access in emergency situations.
Although Israel did not cite an emergency situation, the United States decided to draw some munitions from the stockpile anyway to rotate out older arms. "This is simply a rotating (of) munitions out of the stockpile in order to get newer munitions placed in there," Warren said. (Reporting by Phil Stewart; Additional reporting by Eric Beech; Editing by David Storey, Bernard Orr)