By Matt Spetalnick and Isabel Coles
WASHINGTON/ARBIL, Iraq, Aug 7 (Reuters) - President Barack Obama said on Thursday he had authorized U.S. air strikes to blunt the onslaught of Islamist militants in northern Iraq and began airdrops of supplies to besieged religious minorities to prevent a "potential act of genocide."
Obama, in his most significant response yet to the crisis, said he approved "targeted" use of air power to protect U.S. personnel if Islamic State militants advance further toward Arbil, the capital of the Kurdish semi-autonomous region in northern Iraq, or threaten Americans anywhere in the country.
He said air strikes, which would be the first carried out by the U.S. military in Iraq since its withdrawal in 2011, could also be used if necessary in support of Iraqi and Kurdish forces trying to break the Islamists' siege of a mountaintop where tens of thousands of civilians are trapped.
"Earlier this week, one Iraqi in the area cried to the world, 'There is no one coming to help'," said Obama, who had been reluctant to deepen U.S. military re-engagement in Iraq.
"Well, today America is coming to help."
In late-night remarks televised from the White House to a war-weary American public, Obama insisted he would not commit ground forces and had no intention of letting the United States "get dragged into fighting another war in Iraq."
Obama took action amid international fears of a humanitarian catastrophe engulfing tens of thousands of members of Iraq's minority Yazidi sect driven out of their homes and stranded on Sinjar mountain under threat from rampaging militants of Islamic State, an al Qaeda splinter group.
Many Iraqi Christians have also fled for their lives.
"We can act carefully and responsibly to prevent a potential act of genocide," said Obama, who described the militants as "barbaric."
Obama was responding to urgent appeals from Iraqi and Kurdish authorities to help halt Islamic State's relentless advance across northern Iraq and to deal with the unfolding humanitarian crisis.
However, questions were quickly raised in Washington about whether selective U.S. attacks on militant positions and humanitarian airdrops would be enough to shift the balance on the battlefield against the Islamist forces.
"I completely support humanitarian aid as well as the use of air power," Republican Senator Lindsey Graham tweeted after Obama's announcement. "However the actions announced tonight will not turn the tide of battle."
BLACK FLAG OVER CHECKPOINT
The reason for U.S. alarm was clear.
Reuters photographs on Thursday showed what appeared to be Islamic State fighters controlling a checkpoint at the border area of the Kurdistan, little over 30 minutes' drive from Arbil, a city of 1.5 million that is headquarters of the Kurdish regional government and many businesses.
The fighters had raised the movement's black flag over the guard post. However, a Kurdish security official denied that the militants were in control of the Khazer checkpoint. The regional government said its forces were advancing and would "defeat the terrorists," urging people to stay calm.
Obama, who has carefully avoided direct involvement in most other recent Middle Eastern crises, made clear that preventing a humanitarian catastrophe and averting the threat to American lives and interests in Kurdistan were ample justification for the use of U.S. military power.
However, seeking to keep some pressure on Iraqi Prime Minister Nuri al-Maliki, Obama insisted on the need for an Iraqi government that "represents the legitimate interests of all Iraqis" in order to reverse the militants' momentum.
With the refugees on the mountaintop desperately short of food, water and medicine, U.S. aircraft began dropping emergency aid in the area shortly before Obama spoke on Thursday.
"When we have the unique capabilities to help avert a massacre, then I believe the United States of America cannot turn a blind eye," Obama said.
The Defense Department said U.S. planes dropped 72 bundles of supplies, including 8,000 ready-to-eat meals and thousands of gallons of drinking water for threatened civilians near Sinjar.
It said the planes flew from several air bases in the region and included one C-17 and two C-130 transport planes escorted by two F/A-18 Hornet fighter planes. They were over the drop area for less than 15 minutes, flying at low altitude.
"We intend to stay vigilant and take action if these terrorist forces threaten our personnel or facilities anywhere in Iraq, including our consulate in Arbil and our embassy in Baghdad," Obama said.
He sent in a small number of U.S. military advisers in June to help the Iraqi government's efforts to fend off the Islamist militant offensive but he was reluctant to take direct military action. He had put the onus on Maliki, a Shi'ite Muslim, to form a more inclusive government to help defuse the crisis.
Washington's calculus appeared to shift after Islamic State, which routed the Iraqi military in the north and seized a broad swath of territory in recent months, made recent gains against Kurdish forces and moved toward Arbil.
The decision on air strikes came after urgent deliberations by a president who won the White House in 2008 on a pledge to disentangle the United States from the long, unpopular Iraq war.
Until this week, most of Kurdistan had been protected by its own armed forces, called the peshmerga. Hundreds of thousands of Iraqis fleeing the Islamists, including Christians, Yazidis and others, have taken refuge in the Kurdish area.
The Islamic State's Sunni Muslim militants have swept across northwestern Iraq in recent weeks. The Islamic State views as infidels Iraq's majority Shi'ites and minorities such as Christians and Yazidis, a Kurdish ethno-religious community.
Sunni militants captured Iraq's biggest Christian town, Qaraqosh, prompting many residents to flee in fear that they would be subjected to the same demands they made in other captured areas: leave, convert to Islam or face death.
U.N. Secretary-General Ban Ki-moon said he was "deeply appalled" by the attacks by Islamic State militants. The U.N. Security Council condemned the group and called on the international community to support the Iraqi government.
French President Francois Hollande's office said after he spoke by telephone with Kurdistan president Masoud Barzani that Paris was prepared to support forces engaged in the defence of Iraqi Kurdistan. It did not say how.
A senior U.S. official said Washington was expediting military assistance to Kurdish peshmerga troops.
Shares in energy companies operating in Iraqi Kurdistan plummeted on news of the sweeping Islamist advance toward oilfields in the region.
The militants inflicted a humiliating defeat on Kurdish forces in the weekend sweep, prompting tens of thousands of Yazidis to flee. A Kurdish government security adviser said its forces had staged a tactical withdrawal.
The Kurdish Regional Government's Ministry of Interior said in a statement that "our victory is close."
Some of the many thousands trapped on Sinjar mountain have been rescued in the past 24 hours, a spokesman for the U.N. Office for the Coordination of Humanitarian Affairs said, adding that 200,000 had fled the fighting.
Many of the displaced urgently need water, food, shelter and medicine, he said before the U.S. airdrops began. A spokesman for the U.N. agency for children said many on the mountain were suffering from dehydration and at least 40 children had died.
Yazidis are regarded by the Islamic State as "devil worshippers" and risk being executed by militants seeking to establish an Islamic empire and redraw the Middle East map.
The plight of fleeing Christians prompted Pope Francis to appeal to world leaders to help end what the Vatican called "the humanitarian tragedy now under way" in northern Iraq.
The Islamic State poses the biggest threat to Iraq's integrity since the fall of Saddam Hussein in 2003. Its fighters and their Sunni allies also control a big chunk of western Iraq.
The group has deepened sectarian tensions, pushing Iraq back to the dark days of the civil war that peaked in 2006-2007 under U.S.-led occupation.
The Islamic State's gains have prompted Maliki to order his air force to help the Kurds, whose reputation as fearsome warriors was called into question by their defeat.
Critics blame Maliki for Iraq's crisis, accusing him of promoting the interests of fellow Shi'ites at the expense of Sunnis. Heavily armed Sunni tribes support the Islamic State, although they do not share its ideology. (Additional reporting by Roberta Rampton, Missy Ryan and Mark Felsenthal in WASHINGTON, Tom Miles in GENEVA and James Mackenzie in ROME; Writing by Matt Spetalnick and Michael Georgy; Editing by Paul Tait)