Barack Obama looking to help government after Isis seizes Mosul and Tikrit and closes on Baghdad while Kurds take Kirkuk

Barack Obama has set the stage for renewed US military action in Iraq after the authorities in Baghdad proved powerless to stop relentless Islamist insurgents from seizing further swaths of a country in danger of breaking apart.

The US president said his national security chiefs were looking at any and every way they could help the Iraqi authorities take the fight to thousands of Sunni jihadists who have seized three of the country's biggest cities and vowed to march on Baghdad.

"We do have a stake in making sure that these jihadists are not getting a permanent foothold in either Iraq or Syria, for that matter," Obama said, adding that there were "short-term, immediate things that will need to be done militarily – and our national security team is looking at all the options".

US troops withdrew from Iraq in late 2011 after an eight-year occupation of the country that began with the 2003 invasion. White House officials said the president did not envision any circumstances in which ground troops could return to the country. Air strikes, however, are under active consideration. On Thursday the US began airlifting planeloads of its citizens from Iraq.

Kurdish fighters poured into the disputed northern city of Kirkuk to head off the militants from Isis, the Islamic State in Iraq and the Levant, whose fighters have surged through the north in recent days, encountering little or no resistance from Iraqi army troops who have deserted in their thousands. Isis took the town of Dhuluiyah and was within 60 miles of the capital, local people said. Hundreds of thousands of people have been uprooted by the militant advance. The UN security council was meeting to discuss the sudden crisis.

The Iraqi prime minister, Nouri al-Maliki, offered no reaction as the cities of Mosul and Tikrit fell from his control in the space of three days. He failed to achieve a quorum in parliament needed to impose a state of emergency, and also failed to win the numbers to ask the UN for air strikes and drone attacks against Isis.

The streets of Baghdad were eerie and empty as Isis members took to social media taunting residents that they were advancing towards the capital. Local people have been stockpiling food, fearing that a much talked about enemy is almost at the city's gates.

"They are only 40 miles away," said Fadhil Muthanar, a trader in east Baghdad. "They are hiding in the reeds, in the ruins, waiting to come to the capital. And the Iraqi army can do nothing. Perhaps it will defend the Green Zone [seat of power]. But nothing more. God help us all."

Iraqi officials estimate the total number of Isis forces in Iraq at around 6,000, spread between Mosul, Ramadi, Falluja, Tikrit and the surrounding countryside.

Isis has been handing out flyers in the towns it has seized assuring residents who have remained that it is there to protect their interests. The campaign for hearts and minds is gaining some traction, with some residents railing against perceived injustices at the hands of the Shia majority government. But on Thursday it said it would introduce sharia law in Mosul and other towns, warning women to stay indoors and threatening to cut off the hands of thieves. "People, you have tried secular regimes ... This is now the era of the Islamic State," it proclaimed.

Among those who took control of Tikrit were large numbers of former Ba'ath party members. Ba'athists were the cornerstone of Saddam Hussein's regime and have been persecuted ever since. Residents of Tikrit said some insurgents were wearing the drab green military fatigues worn by Saddam's army. "There are no Isis flags in town," said one local woman. "They are playing Saddam and Ba'ath party songs."

The Kurdish regional government, which has made much of its autonomy since Saddam was toppled, dismissed the prospect of Isis fighters advancing into its seat of power. A Kurdish minister, Sheikh Jaafar Mustafa, said: "This will not happen because we will defend Kirkuk to the last drop of our blood, and I am sure the youth will voluntarily defend that part of Kurdistan."

Kurdish commanders and officials could barely hide their euphoria after being handed a reason to seize Kirkuk – an ethnically contested enclave at the heart of tensions between Baghdad and Erbil since well before 2003. In scenes reminiscent of the fall of Baghdad 11 years ago, Kurdish troops, known as peshmerga, stood by as Kurds and local people looted Iraqi security bases in Kirkuk, carrying away weapons and office furniture, and driving off with armoured humvees. Some peshmurga appeared to join in the looting.

In open defiance of Baghdad, to which the KRG is notionally subservient, Mustafa said the peshmerga felt free to travel anywhere in the country. "Sending peshmerga to any part of Iraq has to be according to plan and on the formal orders of the Kurdish president, who is the commander of Kurdistan's armed forces," he said. "Then the peshmerga will be ready to go anywhere."

While happy to celebrate the symbolism implicit in controlling Kirkuk, Kurdish leaders were reluctant to frame the move as a leap towards a claim for statehood. But with central governance collapsing, Baghdad fears that the Kurds will, at the very least, consolidate control of Kirkuk.

Peshmerga forces mocked the Iraqi army on Thursday, holding up uniforms and weapon clips that troops had discarded as they fled. Most Kurds were driven out of Kirkuk during the Saddam years and only limited numbers have been able to return since the fall of the ousted dictator and the turbulent years that have followed. A mooted referendum on the province has long been delayed. Large oilfields near the city remain targets of the insurgents who aim to cause as much disruption as possible to state utilities.

In nearby Samara, where insurgents have been negotiating with Iraqi army officials, car dealer Taher Hassan said militants had turned up on Sunday and quickly taken control of most of the city.

He said: "All the local police forces have pulled out of their bases in the city. The fighters are negotiating with the tribes who are in charge of the two shrines so they can try to convince army forces near the shrine to hand themselves over without a fight.Everyone in Samara is happy with the fighters' management of the city. They have proved to be professional and competent. The fighters themselves did not harm or kill anyone as they swept forward. Any man who hands over his arm is safe, whatever his background. This attitude is giving a huge comfort to people here. We have lived enough years of injustice, revenge and tyranny and we can't stand any more."

In Washington, officials were scrambling to put together a repsonse, apparently taken aback by the speed and scale of the uprising. "We are actively considering requests from the Iraqi government to assist in this very serious situation," press secretary Jay Carney told reporters. The administration said that vice president Joe Biden had spoken to Maliki by telephone and pledged US support.

The administration argues the responsibility for security rests primarily with the Iraqi government and the White House repeated its earlier criticism of Maliki for his failure to secure national support with more inclusive policies.

"The fact is we can't be everywhere at all times to meet the challenge faced by extremist groups like Isis," Carney said when pressed on why the US was not doing more.

Fazel Hawramy in Kirkuk and Mona Mahmood contributed to this report.