WASHINGTON - The Islamic State militant group has committed genocide against minority Christians and Yazidis as well as Shi'ite Muslims, US Secretary of State John Kerry said on Thursday, a finding that is unlikely to greatly change US policy toward the group."The fact is that Daesh kills Christians because they are Christians. Yazidis because they are Yazidis. Shi'ites because they are Shi'ites," Kerry said, referring to the group by an Arabic acronym, and accusing it of crimes against humanity and of ethnic cleansing.While the genocide finding may make it easier for the United States to argue for greater action against the group, it does not create a legal obligation on the United States to do more.On Wednesday, a State Department spokesman Mark Toner said: "Acknowledging that genocide or crimes against humanity have taken place in another country would not necessarily result in any particular legal obligation for the United States."Islamic State militants have swept through Iraq and Syria in recent years, seizing control of large swathes of territory with an eye toward establishing jihadism in the heart of the Arab world.The group's videos depict the violent deaths of people who stand in its way. Opponents have been beheaded, shot dead, blown up with fuses attached to their necks and drowned in cages lowered into swimming pools, with underwater cameras capturing their agony.US President Barack Obama has ordered air strikes against the group but has not made any large commitment of U.S. troops on the ground."It may strengthen our hand getting other countries to help. It may free us against some (legal) constraints, but the reality is that when you are fighting somebody, you don't need another reason to fight them," said Jon Alterman, director of the Middle East program at the Center for Strategic and International Studies, a think tank.