The US is prepared to intensify its support to Iraq to help drive out al-Qaeda-inspired fighters who have seized several cities, President Barack Obama has said.

The president did not rule out air strikes, raising the possibility of the first American military intervention in Iraq since the US-led war ended in 2011.

Obama's statement on Thursday came as fighters from the Islamic State of Iraq and the Levant (ISIL), which has already taken control over major parts of the country, mainly in the north, vowed to target the capital Baghdad.

"Iraq is going to need more help. It's going to need more help from us, and it's going to need more help from the international community," Obama said.

"My team is working around the clock to identify how we can provide the most effective assistance to them. I don't rule out anything, because we do have a stake in making sure that these jihadists are not getting a permanent foothold," he said.

Cities captured

ISIL, which aims to establish an Islamic state that straddles ‎the border of Iraq and Syria. has launched a military campaign in nearly a third of the country along with associated groups.

On Wednesday, the fighters seized Tikrit, 140km northwest of Baghdad, as Iraqi soldiers fled.

The day before, they captured Mosul, Iraq's second-largest city. ISIL and its allies among local tribesmen also hold the city of Fallujah and other pockets of the Sunni-dominated Anbar province to the west of Baghdad.

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About 500,000 people have fled their homes in fear of increased violence from the ISIL takeovers and possible military assaults by the army to retake control over the seized areas.

Speaking to reporters at the White House, Obama said the Iraqis needed to do more to bridge sectarian divides in the country, but he noted military action was needed right away.

"It's fair to say that in our consultations with the Iraqis there will be some short-term immediate things that need to be done militarily, and our national security team is looking at all the options," Obama said.

"But this should be also a wakeup call for the Iraqi government. There has to be a political component to this."

White House spokesman Jay Carney said later that the United States was not contemplating sending ground troops to Iraq.

US withdrawal criticised

American troops have returned home under Obama's tenure. Critics, including Republican Speaker of the House of Representatives John Boehner, said Obama had contributed to the unrest in Iraq by failing to negotiate a deal under which the US would have left a small force there after pulling out troops at the end of 2011.

Boehner urged Obama to deliver military and other aid promised to the government in Baghdad. "What's the president doing? Taking a nap?" he said.

The Obama administration has highlighted recent US support including delivery of 300 Hellfire missiles, millions of rounds of small arms fire, thousands of rounds of tank ammunition, machine guns and other weapons for the Iraqi Security Forces.

"What I think the Iraqi army desperately needs is trainers and mentors on the ground, in limited numbers, who can help to stiffen their resolve and develop them into a more capable, tactical force," Robert Grenier, a former top counter-terrorism Official at the CIA, told Al Jazeera. "It was the removal of those trainers and mentors in 2011 that left the Iraqi army as vulnerable as it is right now."