Gaza militants, reeling from an Israeli military operation, killed three Israelis on Thursday in a rocket attack that is likely to exact a harsh retaliation by Israel.

The casualties were the first since Israel launched its operation on Wednesday with the assassination of Hamas’ top military commander.

Police spokesman Micky Rosenfeld said two Israeli men and a woman died after a rocket struck their four-story apartment building in the southern Israeli town of Kiryat Malachi. A 4-year-old boy was seriously wounded in and two babies lightly wounded in the strike.

Since the Israeli operation started, a total of 13 Palestinians, including four civilians, have been killed and more than 100 people wounded, according to Palestinian medical officials. Among the dead were two children.

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