U.S. President Barack Obama says he has authorized air strikes against Islamic militants in northern Iraq but will not send U.S. troops back to the country, BBC News reports.

He said Islamic State (IS) fighters would be targeted to prevent the slaughter of religious minorities, or if they threaten U.S. interests.

Strikes have not yet begun, but the U.S. 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 or ISIL, has been gaining ground in northern Iraq and Syria for several months. In a rapid advance in June the group took control of the northern city of Mosul and advanced south towards Baghdad. 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, Obama said U.S. military aircraft had already dropped food and water to members of the Yazidi religious minority community trapped on Mount Sinjar by IS fighters.

The Yazidis face starvation and dehydration if they remain on the mountain, and slaughter at the hands of the IS if they flee, officials have warned.

Obama said the U.S. could not turn a "blind eye" to the prospect of violence "on a horrific scale", especially when the Iraqi government had requested assistance.

He said the U.S. would act "carefully and responsibly, to prevent a potential act of genocide".

U.S. air strikes would target IS fighters if they threaten Baghdad or move towards the Kurdish capital of Irbil, where there is a significant presence of U.S. diplomats and military advisers, Obama said, according to the BBC.

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," 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.

Last month, hundreds of Christian families fled Mosul after 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 U.S.-led invasion in 2003.