President Barack Obama has authorized targeted air strikes against Islamic militants in northern Iraq but will not send US troops back to the country.
Barack Obama said Islamic State (IS) fighters would be targeted to prevent the slaughter of religious minorities or if they threaten US interests.
No strikes have been made yet but the US has made humanitarian air drops to Iraqis under threat from the militants.
IS has seized Qaraqosh, Iraq’s biggest Christian town, forcing locals to flee.
The Sunni Muslim group, formerly known as Isis, has been gaining ground in northern Iraq since it launched its onslaught in June.
It now controls large swathes of Iraq and Syria and says it has created an Islamic caliphate in its territory.
Speaking at the White House on Thursday evening, Barack Obama said US military aircraft had dropped food and water to members of the Yazidi religious minority community trapped on Mount Sinjar by IS fighters.
Barack Obama has authorized two operations against Islamic militants in northern Iraq
Officials had warned that the Yazidis faced starvation and dehydration if they remained on the mountain, and slaughter at the hands of the IS if they fled.
Barack Obama said the US could not turn a “blind eye” to the prospect of violence “on a horrific scale”, especially when the Iraqi government had requested assistance.
The president said the US would act “carefully and responsibly, to prevent a potential act of genocide”.
US air strikes would target IS fighters, should they threaten Baghdad or move towards Irbil, where there is a significant presence of US diplomats and military advisers, Barack Obama said.
In addition, he authorized strikes “if necessary” to help Iraqi government forces break the siege at Mount Sinjar and rescue the trapped civilians.
“The only lasting solution is reconciliation among Iraqi communities and stronger Iraqi security forces,” Barack Obama added.
The president spoke hours after the UN Security Council met. UN Secretary-General Ban Ki-moon said he was “deeply appalled” by the situation.
As many as 100,000 Christians are believed to have fled their homes ahead of the IS advance, and most of them are thought to have gone toward the autonomous Kurdistan Region.
Kurdish forces, known as the Peshmerga, have been fighting the IS militants’ advance in the area around Qaraqosh for weeks, but on Wednesday night it appeared they had abandoned their posts.
Last month, hundreds of Christian families fled nearby Mosul after the Islamist rebels gave them an ultimatum to convert to Islam, pay a special tax, or be executed.
Iraq is home to one of the world’s most ancient Christian communities, but numbers have dwindled amid growing sectarian violence since the US-led invasion in 2003.
About 50,000 Yazidis, meanwhile, are thought to have been trapped in the mountains after fleeing the town of Sinjar over the weekend – although the UN says some of them have now been rescued.
Almost 200,000 civilians have been displaced from Sinjar town, the UN Office for the Coordination of Humanitarian Affairs has warned.
Those trapped on the mountain are facing dehydration, and 40 children are reported to have died already.