The leader of a tribe in Iraq's restive Anbar province announced the mass execution as car bombs killed 56 people across the country on Monday.
Initial reports indicate the rockets might have targeted Camp Victory, a former US military installation near the airport.
At least four people have died already, and the Islamic State controls the areas around a dam that supplies fresh water to some of the hardest hit places.
This month marks one year since a US-led coalition began bombing the Islamic State. The air strikes certainly haven't destroyed the group, but they have changed the terms of the conflict.
With a sweeping political reform package, Iraqi Prime Minister Haidr al-Abadi is aiming to dismantle the government put in place following the US invasion in 2003.
The Iraqi move to close border with Jordan to commercial trucking, a part economics and part military effort, is directed against Islamic State militants.
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