Update as of 4:45 a.m. EDT: The al-Quds hospital in Gaza was struck by two tank shells but no one was killed or injured in the attack, Al Jazeera reported.

According to a BBC report, at least 15 people were killed in the Israeli tank fire at the United Nations-run Abu Hussein school in Jabaliya on Wednesday. Israeli officials are reportedly investigating the attack.

Nearly 1,260 Palestinians have reportedly been killed so far as Operation Protective Edge continued for the 23rd day Wednesday, making it the longest-running conflict between Israel and Hamas.

UNRWA is scrambling to accommodate the thousands of Palestinian civilians displaced by the conflict, even as most U.N.-run schools being used as shelters have exceeded maximum capacity.

Israeli shelling in the early hours of Wednesday killed at least 32 people in the Gaza Strip, including 20 at a United Nations-run school being used as a shelter for displaced Palestinians in the Jabaliya refugee camp, Agence France-Presse, or AFP, reported Wednesday.

As the Hamas-Israel conflict entered its 23rd day Wednesday, the death toll in Gaza has crossed 1,200. In its bloodiest day yet, 128 Palestinians were killed in a series of attacks on Tuesday, according to an Associated Press, or AP, report.  On the Israeli side, 53 soldiers and three civilians have been killed since the start of the offensive on July 8.

On Tuesday, UNRWA had reportedly found a cache of rockets stored in one of its schools in Gaza, according to reports. It was not immediately clear whether this was the school that was targeted in the Israeli air strike on Wednesday. 

UN Spokesperson Chris Gunness issued a strong condemnation against the "groups who endangered civilians by placing these munitions in our (U.N.) school," calling it a "flagrant violation of the neutrality of our premises," Reuters reported Tuesday. He did not, however, specifically name the groups responsible.