GAZA CITY, Gaza Strip (AP) -- A Palestinian health official says 13 people were killed after tank shells hit a U.N. school in Gaza where hundreds of Palestinians had taken refuge from Israeli attacks.

Ilia Yefimovich, Getty Images

Gaza health official Ashraf al-Kidra said another 40 Palestinians were wounded in the shelling early Wednesday.

Adnan Abu Hasna, a spokesman for a U.N. aid agency, says tank shells hit the Abu Hussein U.N. school in the Jabaliya refugee camp around 4:30 a.m.

An AP reporter who arrived later at the school saw what appeared to be tank shells in a bathroom and two classrooms.

The incident comes a day after Israel unleashed its heaviest air and artillery assault in the bloodiest day of the three-week Gaza war, destroying key symbols of Hamas control and shutting down the territory's only power plant.

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