Israeli aircraft have fired missiles at an apartment tower in downtown Gaza City, collapsing the 12-story building.
Palestinian officials say at least 22 people were hurt, including 11 children.
The Israeli military says the airstrike targeted a Hamas operations room in the building, but did not explain why the entire tower with 48 apartments was leveled.
Gaza police say Israeli aircraft fired a warning missile at the roof of the building at dusk, followed five minutes later by two missiles with explosives.
The explosion shook nearby buildings and sent a huge fireball into the sky.
Israel has launched some 5,000 airstrikes against Gaza in nearly seven weeks of fighting with Hamas, but today's strike marks the first time an entire high-rise was toppled.
The military says Gaza militants fired at least 93 rockets and mortar shells at Israel today, a day after a mortar shell from Gaza killed a 4-year-old boy in southern Israel.
Israel's defense minister is calling on residents in southern Israel to be ready for a prolonged campaign against Hamas militants.
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