American planes were dropping bombs and bottled water over Iraq yesterday.

Bombs on Islamic State (IS) jihadists that have captured wide swathes of northern Iraq since June. Water on threatened civilians of the country's Yazidi minority trapped on a sweltering, barren mountainside where they have fled in fear of extermination at the hands of the jihadists.

Yesterday, US President Barack Obama made clear that there were no quick fixes to the growing crisis in Iraq.

"This is going to take some time," said Obama, speaking of the military and humanitarian operations ongoing in the region.

Obama's remarks came in the wake of a diplomatic initiative introduced at the UN last week by Britain in response to the rapidly deteriorating situation in Iraq aimed at stymying the establishment of an Islamic caliphate by the jihadists that now extends across the country and into neighbouring Syria. It will also concentrate on quashing the jihadists' illicit oil and gold exports, prevent ransom kidnappings, and hobble recruitment.

"There was deep alarm about the speed of events," was how Britain's UN ambassador, Mark Lyall Grant, summed up the UN Security Council's response when presented with the UK initiative.

The speed of IS's advance suggests that it has been co-operating with a network of Sunni remnants from former Iraqi dictator Saddam Hussein's underground resistance which opposed the Americans after 2003 and has continued to fight against the Shia-dominated Baghdad government of Nouri al-Maliki since the Americans left at the end of 2011.

If the military advance of the IS fighters has been swift it has also been terrifying in equal measure. The brutality that made IS notorious over the course of the Syrian civil war has become a fundamental part of its Iraqi regime.

The Sunni militants, who have beheaded and crucified captives in their drive to eradicate unbelievers, are also proving a military force to be reckoned with.

After routing Kurdish forces last week, IS fighters are just 30 minutes' drive from Erbil, the Kurdish regional capital which up to now has been spared the sectarian bloodshed that has scarred other parts of Iraq for a decade.

According to analysts at the US-based independent intelligence think tank Stratfor, Iraq's Kurdish region faces serious geographic challenges when it comes to defence. Roughly crescent-shaped, the interior of the crescent, which faces Iraq's disputed territories, starts as flat, open desert and steadily elevates into hills.

This puts the defending Kurdish forces at a disadvantage. They have to protect an arcing border that stretches for more than 620 miles, forcing Kurdish troops to travel further to defend their positions while the IS enjoys interior lines of movement.

Additionally, the open land of the desert plays to the IS's strength: mobility. The jihadists can use their fast-travelling technicals - pick-up trucks outfitted with heavy weaponry - and mass quickly on any weak points along the defensive perimeter.

Much of the region's critical energy infrastructure, both within the Kurdistan Regional Government proper and in the disputed regions surrounding Kirkuk, lies near areas of Iraqi territory now claimed by IS militants and in open desert.

Critical cities such as Dohuk, Erbil and Kirkuk are also nestled either within or close to the disputed territories on the crescent's interior border.

Any advance by the IS into Kurdish-controlled territory immediately puts the jihadists dangerously close to these strategic areas because of the lack of geographic depth in this highly contested borderland.

Already IS is said to be in control of the two-mile-wide Mosul Dam. This could prove a critical factor for the millions of Iraqis who live downstream of the facility, all the way down the Tigris to Baghdad.

In effect, IS is in control of what could be a major weapon of mass destruction, one that the US military said in 2006 was, without the help of brutal jihadists, already "the most dangerous dam in the world".

A dam administrator said yesterday that militants were putting up their trademark Islamic State black flags and patrolling with flatbed trucks mounted with machine guns to protect the facility they seized from Kurdish forces earlier last week.

"They are gathering people to work at the dam," the administrator confirmed to reporters by telephone. In their latest offensive, IS has also captured a fifth oilfield, all of which helps fund its military operations,

In the city of Erbil employees of foreign oil firms were being evacuated by air. Local Kurds, meanwhile, were snapping up AK-47 assault rifles in arms markets for fear of imminent attack, although these had been ineffective against the superior firepower of the IS fighters.

Given the IS threat, a source in the Kurdistan Regional Government said it had received extra supplies of heavy weaponry from the Baghdad federal government "and other governments" in the past few days, but declined to elaborate.

The semi-autonomous Kurdish region has, until now, been the only part of Iraq to survive the past decade of civil war without a serious security threat.

Its vaunted "peshmerga" fighters - those who "confront death" - also controlled wide stretches of territory outside the autonomous zone, which served as sanctuary for fleeing Christians and other minorities when IS fighters stormed into the region last month.

But the past week saw the peshmerga crumble in the face of the IS advance during which the jihadists used heavy weapons seized from fleeing Iraqi troops.

With alarm bells ringing in Washington, the US Defence Department said two F/A-18 warplanes from an aircraft carrier in the Gulf had dropped laser-guided 500-pound bombs on IS artillery batteries. Other air strikes targeted mortar positions and an IS convoy.

President Obama said the action was needed to halt the jihadists' advance, protect Americans in the region as well as hundreds of thousands of Christians and members of other religious minorities who have fled for their lives. Speaking at a news conference yesterday, he confirmed that the airstrikes have destroyed arms and equipment that IS fighters could have used to attack Erbil, but warned the current operation in Iraq could take some time.

"I don't think we're going to solve this problem in weeks. This is going to be a long-term project," he told reporters before leaving Washington for a two-week holiday in Massachusetts.

Obama said the United States would continue to provide military assistance and advice to the Baghdad government and Kurdish forces.

But he stressed repeatedly the importance of Iraq forming its own inclusive government.

"I think this a wake-up call for a lot of Iraqis inside of Baghdad recognising that we're going to have to rethink how we do business if we're going to hold our country together," Obama said.

On Thursday, the president authorised the US military to make airdrops of humanitarian assistance to prevent what he called a potential "genocide" of the ancient Yazidi religious sect in Iraq.

Yesterday, US and British military aircraft continued to drop relief supplies to members of the ancient sect, tens of thousands of whom have collected on a desert mountaintop seeking shelter from the jihadists who had ordered them to convert or die. Many have already died of thirst or exposure.

Basim Karim, one of a tiny number of Yazidis who have settled in the United States and who is from Sinjar, spoke recently to Foreign Policy magazine of what had happened to his family.

" They woke up one day to find the Kurdish peshmerga, who once protected their village, gone and the Islamic State in their place.

"They saw dogs dragging around human body parts in the towns before they fled, and there were surely at least 1000 corpses".

Yesterday, a UN relief spokesman said some 200,000 people fleeing the jihadists' advance had reached the town of Dohuk on the Tigris River in Iraqi Kurdistan. Tens of thousands had fled further north to the Turkish border.

Obama also confirmed yesterday that the US is considering with its allies creating a safe humanitarian corridor for the Yazidis to leave the area around Mount Sinjar.

This suggestion was a cause for concern in some US political quarters which believe that such an operation is not possible without "boots on the ground" and that the deployment of any American troops could result in "mission creep".

For now the White House continues to claim there are no military options, only political ones.

"My expectation would be that they wouldn't start an offensive action that didn't have a clear end state," said Jon Alterman, a senior vice-president at the Centre for Strategic and International Studies in Washington.

Alterman believes that despite IS's brutality, the group would not go so far as to provoke a full confrontation with the US military. Sceptics, however, say we have been here before and that the spiralling crises gripping the Middle East could easily draw in a larger scale military intervention by the US and its allies.

The question now is whether the US can stand back while IS creates what is effectively a proto-state on the ungoverned territory straddling the borderlands between Syria and Iraq.

"This is a new, more dangerous strategy since 2011," says Hassan Abu Haniyeh, a Jordanian expert on jihadist movements summing up the crisis in an interview with The Economist magazine.

"If IS manages to hold onto its turf in Iraq, it will control an area the size of Jordan with roughly the same population [some six million], stretching 500km from the countryside east of Aleppo in Syria into western Iraq."

President Obama may be heading for his two week holiday in Massachusetts, but the relentless advance of the IS is sure to weigh heavily on his mind throughout his break and beyond.