As my colleagues report, Palestinian officials and a U.N. agency say Israeli artillery shells on Wednesday hit a U.N.-run school that was sheltering Palestinian families, killing at least 20. A U.N. statement pinned the blame on the Israeli military, which says it's investigating the incident. "Today the world stands disgraced," the statement read.

For Chris Gunness, a spokesman for the United Nations Relief and Works Agency, which has numerous facilities in Gaza, it's all too much. This is the sixth time UNRWA sites have been hit during Israel's current campaign. He broke down sobbing during an interview, footage of which was screened by Al Jazeera Arabic. Watch above.

So far in more than three weeks of fighting, 1,340 Palestinians have died, the majority of whom were civilians, including many women and children. Fifty-three Israeli soldiers have perished, as have three civilians in Israel, one of whom was a farm worker from Thailand.

Earlier in the day, Gunness tweeted these plaintive entreaties: