Prime Minister Tony Abbott has backed US President Barack Obama’s action in Iraq.

President Obama has authorised US air strikes on Iraq and humanitarian supply drops to prevent a “genocide” by Islamist extremists against minorities.

Islamist militants are surging across the north of the country toward the capital of the Kurdish region, Erbil, sending tens of thousands of Christians fleeing for their lives.

Mr Abbott said the terrorist group Islamic State, formerly known as ISIL or ISIS, had emerged as a major threat in Syria and Iraq.

“If it is allowed to succeed in carving out a terrorist state in the Middle East it will also pose a significant threat to international security,” Mr Abbott said in a statement on Friday.

He understood the air strikes were intended to support US personnel located in Erbil and also to break the ISIL siege of Sinjar.

“The Australian government is extremely concerned by the threat posed by ISIL and the even greater threat it will pose if it succeeds in its latest offensive,” Mr Abbott said.

“Therefore we strongly support President Obama’s course of action.”

He said it was no longer an evil terrorist group but a “highly potent insurgent army” capable of holding territory, imposing its “abhorrent form of government” and forging alliances with other extremist organisations.

Barack Obama gives green light to bombings

Mr Obama said American warplanes would attack Islamic State “terrorist convoys” if they tried to advance on Erbil.

“In recent days these terrorists have continued to move across Iraq and have neared the city of Erbil where American diplomats and civilians serve at our consulate and American military personnel advise Iraqi forces,” he said.

“I’ve directed our military to take targeted strikes against ISIL [Islamic State] terrorist convoys should they move toward the city. We intend to stay vigilant and take action if these terrorist forces threaten our personnel or facilities anywhere in Iraq including our consulate in Erbil and our embassy in Baghdad.

Mr Obama said warplanes could also be sent into action to save the lives of thousands of members of the Yazidi religious minority, who are trapped on a mountaintop after Islamic State fighters swept into their hometown.

“We can act, carefully and responsibly to prevent a potential act of genocide,” he said.

“I therefore authorised targeted air strikes if necessary to help forces in Iraq as they fight to break the siege and protect the civilians trapped there.”

A US defence official said US planes had already dropped water and food to the Yazidis stranded on Sinjar mountain.

It is understood the aircraft that dropped the humanitarian supplies safely left the immediate drop area near Sinjar before Mr Obama began speaking.

“We’re also providing urgent assistance to Iraqi Government and Kurdish forces so they can more effectively wage the fight against ISIL,” Mr Obama added.

Any US airstrikes would be the first in Iraq since a 2011 pullout of troops.

But the Pentagon has already been forced to deny reports that warplanes have already gone into action.

“Press reports that US has conducted airstrikes in Iraq completely false,” Rear Admiral John Kirby said in a post on his Twitter feed. “No such action taken.”

An image from the Kurdish border area showed what appeared to be Islamic State fighters controlling a checkpoint at the semi-autonomous region, just 30 minutes’ drive from Erbil, 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 the militants were in control of the Khazer checkpoint, and the regional government said its forces were advancing and would “defeat the terrorists,” urging people to stay calm.

Iraqi mourners carry the coffin of a Shiite loyalist fighter. Photo: Getty

Minorities fear death at hands of militants

Earlier this week Islamic State militants captured Iraq’s biggest Christian town, Qaraqosh, prompting many residents to flee, fearing they would be subjected to the same demands the Sunni militants made in other captured areas: leave, convert to Islam or face death.

The Islamic State, considered more extreme than Al Qaeda, sees Iraq’s majority Shiites and minorities such as Christians and Yazidis, a Kurdish ethno-religious community, as infidels.

UN secretary-general Ban Ki-moon said he was “deeply appalled” by reports of attacks by Islamic State militants in Iraq and called on the international community to help the country’s government.

The UN Security Council was due to hold an emergency meeting on the crisis.

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.

The Islamic State said in a statement on its Twitter account that its fighters had seized 15 towns, the strategic Mosul dam on the Tigris River and a military base, in an offensive that began during the weekend.

Kurdish officials say their forces still control the dam, Iraq’s biggest.

On Thursday, two witnesses said Islamic State fighters had hoisted the group’s black flag over the dam, which could allow the militants to flood major cities or cut off significant water supplies and electricity.

The Kurdish Regional Government’s Ministry of Interior said in a statement that “our victory is close.”

Thousands stranded on Sinjar mountain

The militants’ weekend capture of Sinjar, ancestral home of the Yazidi minority, prompted tens of thousands of people to flee to surrounding mountains, where they are at risk of starvation.

Yazidis, regarded by the Islamic State as “devil worshippers”, risk being executed by the Sunni militants seeking to establish an Islamic Caliphate and redraw the map of the Middle East.

“This is a tragedy of immense proportions, impacting the lives of hundreds of thousands of people,” spokesman David Swanson said by telephone.

Many of the displaced people urgently need water, food, shelter and medicine, he said.

A spokesman for the UN agency for children said many of the children on the mountain were suffering from dehydration and at least 40 had died.

Thousands of Iraqis, most of them Yazidis, are streaming to the border with neighbouring Turkey to flee the fighting, Turkish officials said.

Gains by the Islamic State have raised concerns that militants across the Arab world will follow their cue.

During the weekend, the Sunni militants seized a border town in Lebanon, though they appear to have mostly withdrawn.

The Islamic State poses the biggest threat to Iraq’s integrity since the fall of Saddam Hussein in 2003.

The group has deepened sectarian tensions, pushing the country back to the dark days of the civil war that peaked in 2006-2007 under US-led occupation.