The Obama administration declared Thursday that rapes, killings and repression of minorities in Iraq and Syria by Islamic State militants constitute genocide.
Secretary of State John F. Kerry said the region's Christians, Yazidis and Shiite Muslims were victims of genocide -- the deliberate and systematic elimination of a group -- and ethnic cleansing.
"Daesh is responsible for genocide against groups in areas under its control, including Yazidis, Christians and Shia Muslims," Kerry, using an Arabic acronym for Islamic State, said in announcing his determination.
"Daesh is genocidal by self-proclamation, by ideology and by actions -- in what it says, what it believes and what it does."
Elevating the characterization of Islamic State's litany of atrocities to genocide would normally imply robust action to stop the radical group.
The Obama administration did not announce new initiatives but said ongoing military and political activities, including airstrikes and propaganda campaigns, would be intensified.
"Is [the determination] going to trigger something new? No," State Department spokesman John Kirby said. "But [genocide] is part and parcel of how we have been thinking of this for nigh-on a year."
Kerry noted that Islamic State has also in some cases attacked Kurds and Sunni Muslims.
"The fact is that Daesh kills Christians because they are Christians, Yazidis because they are Yazidis, Shia because they are Shia," Kerry said.
"This is the message it conveys to children under its control. Its entire worldview is based on eliminating those who do not subscribe to its perverse ideology."
Thursday was a congressionally mandated deadline for the State Department to pronounce whether genocide was being committed in Syria and Iraq, where Islamic State fighters have taken over vast areas thanks to chaos and warfare.
The level of their brutality has shocked even hardened observers, given the militants' penchant for videotaping beheadings, the burning or drowning alive of victims, and other chilling slayings.
The U.S. House of Representatives this week declared Islamic State's actions to be genocide, possibly putting pressure on Kerry to act.
It is the first time the U.S. has made a genocide declaration since 2004, when then-Secretary of State Colin L. Powell determined that violence in Sudan's Darfur region deserved similar classification.
Human rights groups immediately praised Kerry's decision and urged Congress to agree to receive more refugees from the region.