JERUSALEM — A U.S.-based rights group says Israel violated laws of war in a series of airstrikes during an eight-day military operation last November against the Hamas militant group in the Gaza Strip.

Human Rights Watch (HRW) says it counted 14 airstrikes in which there didn't appear to be a valid military target, and four others targeting militants, but which used disproportionate force.

HRW says the attacks killed more than 40 Palestinian civilians. It cites a bomb attack on a Gaza home that killed a father and two children, ages 4 and 2. The group released the report late Tuesday.

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Israel's air assault came after increased rocket fire and other attacks by Gaza militants.

The military had no immediate comment. In the past, it has accused Hamas of using civilians for cover.