The US says the Islamic State (IS) group has committed genocide against Yazidis, Christians and Shia Muslims.
US Secretary of State John Kerry said IS was “genocidal by self-proclamation, by ideology and by actions”.
He also said the group was responsible for crimes against humanity and ethnic cleansing in areas it controls in Syria and Iraq.
“Naming these crimes is important, but what is essential is to stop them,” Mr Kerry added.
Mr Kerry admitted that a lack of access to IS areas meant the US did not have a “complete picture” of the atrocities that had been carried out.
He said the “full facts” must be sought, and the US would “strongly support” efforts to collect evidence of IS atrocities and brings those responsible to account.
“The fact is that Daesh kills Christians because they are Christians, Yazidis because they are Yazidis, Shia because they are Shia,” he said.
“This is the message it conveys to children under its control. Its entire world view is based on eliminating those who do not subscribe to its perverse ideology.”
Genocide is defined by the UN Convention as “acts committed with intent to destroy, in whole or in part, a national, ethnic, racial or religious group”.
It is understood by most to be the gravest crime against humanity it is possible to commit.