As impatient lawmakers and religious groups step up calls for action, Secretary of State John Kerry is leaning toward making the determination and could do so as early as next week, when a congressional deadline for action has been set, according to several administration officials.
However, the officials cautioned that a legal review is still under way and said it is likely Kerry will not meet the March 17 deadline.
The House will vote on Monday on a bill that would identify the Islamic State's actions against Christians, Yezidis and other groups, including the Kurds, as "genocide, war crimes and crimes against humanity."
It would also mark only the second time a US administration has reached that conclusion while a conflict is ongoing.
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The first was in 2004 when Secretary of State Colin Powell determined that atrocities being committed in Sudan's Darfur region constituted genocide.
Powell reached that determination amid much lobbying from human rights groups but only after State Department lawyers advised him that it would not, contrary to legal advice offered to previous administrations, obligate the United States to take action to stop it.
Powell instead called for the UN Security Council to appoint a commission to investigate and take appropriate legal action if it agreed with the genocide determination.
Kerry faces similar issues.
Although the United States is already involved in military strikes against the Islamic State and has helped prevent some incidents of ethnic cleansing, notably of Yezidis, some argue that a genocide determination could require additional US action.
At the least, a determination would probably be accompanied by a referral to the Security Council for possible prosecution by either the International Criminal Court or another tribunal that might be set up specifically for Syria and Iraq.