US Secretary of State John Kerry slammed the Islamic State group for "abhorrent" abuses after the jihadists boasted of selling captured women and girls as slaves.
Islamic State militants said abducted Yazidi women and children had been divided among its fighters according to sharia law.
Kerry described the act as despicable, and said the group "does not represent Islam."
"ISIL now proudly takes credit for the abduction, enslavement, rape, forced marriage and sale of several thousand... women and girls, some as young as 12 years old," Kerry said in a statement, referring to an alternative name for the jihadists.
"ISIL rationalizes its abhorrent treatment of these women and girls by claiming it is somehow sanctioned by religion. Wrong. Dead wrong."
Tens of thousands of Yazidis, a minority population mostly confined to northern Iraq, have been displaced by the four-month-old jihadist offensive in the region.
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The United States has been leading an air campaign against the Islamic State group in Iraq since August 8.
Yazidi leaders and rights groups have said the community faces genocide, which was put forward by Washington as a reason for the military campaign.
Kerry called on the international community to condemn the "commodification of women and children as spoils of war, including through their subjection to horrific physical and sexual violence, intimidation, and deprivation of liberty."
He said the Islamic State group represented "the worst of humanity," contrasting its actions with those of recent Nobel Peace Prize winners Malala Yousafzai and Kailash Satyarthi.
Rights watchdog Amnesty International accused the Islamic State organization of widespread abuses, and said its members are committing war crimes.
Military commanders from the US-led coalition fighting the group -- which now includes around 60 countries -- met in Washington Tuesday to discuss the military campaign.
The White House said it was "succeeding" in its strategy to defeat the militants, who have taken over swaths of territory in Iraq and Syria.