The White House on Thursday said it was ready to support an investigation by the International Criminal Court into alleged genocide carried out by ISIS in Syria and Iraq.
"The United States will cooperate with independent efforts to investigate genocide," said spokesman Josh Earnest, adding that the administration is willing to support the ICC in gathering evidence.
"The ICC is typically the organization that would take a look at this, and given the judgment that Secretary (of State John) Kerry has made, the United States would be supportive of that effort, both rhetorically, but also in a tangible way as well," said Earnest.
"The United States will support efforts to collect documents, preserve and analyze evidence of atrocities and the United States will do all we can to ensure perpetrators of these atrocities are held to account and brought to justice."
The United States is not party to the ICC, but President Barack Obama's administration has introduced a policy of working with the court.
The US declared earlier Thursday that ISIS's slaughter of Christians, Yazidis and Shiites in Iraq and Syria amounts to a genocide and vowed to halt it.
"Daesh is genocidal by self-proclamation, by ideology and by actions, in what it says, what it believes and what it does," Secretary of State John Kerry said.
"Daesh is also responsible for crimes against humanity against these same groups," he added, using the US government's preferred term for the group.
"Naming these crimes is important, but what is essential is to stop them," Kerry said.
The declaration was made based on a review of the information gathered by the US State Department, intelligence community and outside groups, Kerry said, adding: "I want to be clear. I am neither a judge, nor a prosecutor, nor jury with respect to the allegations of genocide, crimes against humanity and ethnic cleansing by specific persons. Ultimately, the full facts must be brought to light by an independent investigation and through a formal legal determination by a competent court or tribunal."
However, he said, the US would strongly support efforts to collect, document, preserve and analyse the evidence of atrocities and would do all it can to make sure that perpetrators are brought to justice.
"I hope that my statement today will assure the victims of Daesh' atrocities that the United States recognizes and confirms the despicable nature of the crimes that have been committed against them," Kerry said. "Second, I hope it will highlight the shared interest of the otherwise diverse groups have in opposing Daesh."
Earlier this week, the US House of Representatives passed a non-binding resolution by a vote of 393-0 designating ISIS's murders of religious minorities genocidal, a move which has international legal implications – as the later White House announcement demonstrated.
The United States is already leading a coalition of Western and Arab allies to strike ISIS targets from the air and to support Iraqi government and Kurdish and Syrian militia forces against the group.
ISIS has in recent months suffered seriously losses, particularly in northern Syria to Kurdish forces, but continues to hold large swathes of land in both Syria and Iraq.
AFP contributed to this report