Israel’s military on Wednesday attacked a second United Nations school packed with Palestinian refugees and later a busy marketplace, killing scores of civilians and injuring hundreds more in what witnesses called one of the most violent days in the weeks-long offensive against Hamas in the Gaza Strip. The market attack occurred during a temporary cease-fire that Israel had earlier declared in areas where it was not conducting military operations. A U.N. aid spokesman confirmed that tank shells hit the U.N. school in the Jabaliya refugee camp at around 4:30 a.m. The explosions tore through two classroom walls, killing at least 16 people and wounding more than 90 others. "Last night, children were killed as they slept next to their parents on the floor of a classroom in a U.N. designated shelter in Gaza," Pierre Krahenbuhl, United Nations Relief and Works Agency (UNRWA) commissioner-general, said in a statement.

Click here for the latest news and analysis “Children killed in their sleep; this is an affront to all of us, a source of universal shame. Today the world stands disgraced," he said. More than 200,000 displaced Palestinians, many heeding Israeli evacuation orders, have taken shelter in U.N. schools and buildings across the besieged territory. The U.N. said it had communicated to the Israeli military 17 times before Wednesday’s attack — including once just hours before the fatal shelling — that thousands of internally displaced Palestinians had sought refuge in the school. The White House condemned the school shelling, but did not assign responsibility for the attack to either Israelis or Palestinians. Meanwhile, the Pentagon confirmed that the U.S. has agreed to replenish Israel's dwindling supplies of mortar rounds and grenade launchers. Wednesday's shelling marks the sixth time a U.N. school has been targeted by the Israeli military during its latest offensive in the Gaza Strip, and the second time such an institution has been destroyed. "We have visited the site and gathered evidence," Krahenbuhl's statement said, adding that "our initial assessment is that it was Israeli artillery that hit our school, in which 3,300 people had sought refuge. We believe there were at least three impacts." The Israeli military said it was still investigating the incident, and in a brief statement said Palestinian fighters near the facility had fired mortar bombs and Israeli forces had shot back. "Earlier this morning, militants fired mortar shells at [Israeli] soldiers from the vicinity of the UNRWA school in Jabaliya. In response, soldiers fired towards the origins of fire, and we're still reviewing the incident," a military spokeswoman said.

Shujayea market attack

Hours after Israeli forces attacked the U.N. school, they launched an assault on a busy market in the Gaza Strip town of Shujayea, killing at least 15 people and wounding more than 160, Gaza’s Health Ministry said. Many of the victims appeared to have been shopping at the time of the attack. The number of casualties is expected to rise, local authorities said. The Shujayea market attack followed a separate market attack near Jabaliya refugee camp earlier on Wednesday that left six people dead. The latter attack occurred during a four-hour cease-fire that Israel unilaterally declared in areas where its soldiers were not operating. "The humanitarian window will not apply to the areas in which IDF [Israeli Defense Forces] soldiers are currently operating," a military statement said. It added that the nearly 250,000 residents displaced by Israel's offensive could not immediately return to their homes. Many Gazans apparently believing that they were protected by the cease-fire, and had gone to the Shujayea market to stock up on supplies to see them through another night of possible bombardment. Due to an Israeli attack on Gaza's only power plant on Tuesday, 90 percent of the territory's 1.8 million people were without electricity. In addition to residents' inability to refrigerate food and pump water, the power cut is expected to affect hospitals and sewage-treatment facilities. Hamas characterized the Shujayea market attack as a "massacre," saying in a statement that Israel was committing "mass murder and deliberate acts of revenge after failing to make military progress" against Palestinian resistance groups, including Hamas and Islamic Jihad. Israel's weeks-long military offensive in Gaza has claimed the lives of more than 1,361 Palestinians — most of them civilians — according to the Gaza Health Ministry. Israeli fatalities number 59, including two civilians. A Thai foreign worker has also been killed in the violence.

Elusive cease-fire