In a speech on the White House lawn yesterday, he signalled there would be no quick fix as he also revealed that US air strikes in northern Iraq had destroyed arms that Islamic State militants could have used against Iraqi Kurds.
Obama also said it would take more than bombs to restore stability and criticised Iraqi prime minister Nouri al-Maliki’s Shiite-led government for failing to empower Sunnis.
He told a news conference: “I don’t think we’re going to solve this problem in weeks. This is going to take some time.”
Islamic State, known as Isis or IS, has captured swathes of northern Iraq since June, executing non-Sunni captives, displacing tens of thousands of people and drawing the first US air strikes in the region since Washington withdrew American troops in 2011.
After routing Kurdish forces last week, the militants were yesterday just 30 minutes’ drive from Irbil, the Iraqi Kurdish capital, which had been spared the sectarian bloodshed that has scarred much of Iraq for a decade.
Obama said Washington would continue to provide military assistance and advice to Baghdad and Kurdish forces, but stressed repeatedly the importance of Iraq, which is a major oil exporter, forming its own inclusive government.
Maliki has been widely criticised for authoritarian and sectarian policies that have alienated Sunnis and made some support the insurgency.
“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, before leaving for a two-week holiday.
He also dismissed the suggestion that renewed military intervention in Iraq might cause him to regret pulling out troops in the first place.
Employees of foreign oil firms in Irbil have been leaving, and Kurds have snapped up AK-47 assault rifles in arms markets for fear of imminent attack, although these had been ineffective against the superior firepower of the Islamic State fighters.
Given the Islamic State 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.
In their latest advance, Isis seized a fifth oilfield, several towns and Iraq’s biggest dam, sending tens of thousands fleeing for their lives.
An engineer at the Mosul dam said Islamic State fighters had brought in engineers to repair an emergency power line to the city, Iraq’s biggest in the north, that had been severed four days ago, causing power cuts and water shortages. “They are gathering people to work at the dam,” he said.
A dam administrator said militants were putting up distinctive Isis black flags and patrolling with flatbed trucks mounted with machine guns to protect the facility they seized from Kurdish forces earlier this week.
Isis, comprised mainly of Arabs and foreign fighters who want to reshape the map of the Middle East, pose the biggest threat to Iraq since Saddam Hussein was toppled by a US-led invasion in 2003.
The Sunni militants, who have beheaded and crucified captives in their drive to eradicate unbelievers, first arrived in northern Iraq in June from Syria where they have captured wide tracts of territory during a three-year civil war. Almost unopposed by US-trained Iraqi government forces who fled by the thousands, the insurgents swept through the region and have threatened to march on Baghdad with Iraqi military tanks, armoured personnel carriers and machine-guns they seized.
On Friday the US defence department said two F/A-18 Hornet warplanes from an aircraft carrier in the Gulf had dropped laser-guided 500lb bombs on Isis artillery batteries. Other air strikes targeted mortar positions and an Isis convoy.
Obama has said the action was needed to halt the Islamist advance, protect Americans in the region as well as hundreds of thousands of Christians and members of other religious minorities at risk.
US military aircraft dropped relief supplies to members of the ancient Yazidi sect, tens of thousands of whom have collected on a desert mountaintop seeking shelter from insurgents who had ordered them to convert to Islam or die. Isis militants have threatened to kill more than 300 Yazidi families in the villages of Koja, Hatimiya and Qaboshi unless they change religion, witnesses said.
British aircraft would also drop humanitarian supplies “imminently” to help the Yazidi, said Foreign Secretary Philip Hammond. “We expect that to go on for the foreseeable future, dropping supplies to people, in particular to the people who are trapped on the mountain Sinjar,” he said.
“We are more widely looking at how to support this group of people and get them off that mountain.”
The Isis advance has returned Iraq to levels of violence not seen since a civil war peaked in 2006-07 during the US occupation. The territorial gains of Islamic State, which also controls a third of Syria and has fought this past week inside Lebanon, has unnerved the Middle East and threatens to shatter Iraq, a country split between mostly Shiites, Sunnis and Kurds.
Attention has focused on the plight of Yazidis, Christians and other minority groups in northern Iraq, one of the most demographically diverse parts of the Middle East for centuries.
The Christians are mostly Chaldeans, part of the Catholic Church. Their numbers have fallen from around 1.5 million since the 2003 invasion to less than 450,000.
The Yazidis – around 50,000 have been trapped by the Islamic State advance – are a secretive group whose origins and ethnicity are subject to continuing debate. Their religion incorporates elements of many faiths, including Zoroastrianism, Christianity and Islam. Many Muslims and other groups view Yazidis as devil worshippers.
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 – hardened by years of fighting Saddam Hussein’s forces – also controlled wide stretches of territory outside the autonomous zone, which served as sanctuary for fleeing Christians and other minorities when Isis fighters stormed into the region last month.
But the past week saw the peshmerga crumble in the face of Isis fighters, who have heavy weapons seized from fleeing Iraqi troops and are flush with cash looted from banks.