President Barack Obama's war strategy failed to stop Islamic State jihadists from overrunning Ramadi but he appears reluctant to change course despite the group's advances on the battlefield.

The disastrous fall of the Iraqi city exposed the limits of Obama's policy, experts say, highlighting the sectarian divisions in Iraqi society exploited by the IS group and the American president's determination to avoid another protracted military occupation.

After the Iraqi army's embarrassing rout on Sunday, Obama struggled to defend his approach and insisted the collapse in Ramadi was merely a "tactical setback."

"I don't think we're losing," Obama said in an interview with The Atlantic.

Obama said the question was not whether or not to send in US ground troops but "how do we find effective partners" that can defeat the Sunni extremists in Iraq and Syria.

But, even inside his administration, the result in Ramadi was seen as damaging for both the Iraqi government and the US-led coalition backing it with air strikes since late last year.

Only days after Ramadi was overrun, the jihadists also seized the ancient city of Palmyra in Syria as well as a key border crossing, undercutting weeks of optimistic talk from the Pentagon that the extremists were "on the defensive."

With IS still on the move after more than 4,000 US-led air strikes in nine months in Iraq and Syria, the administration was taking a "hard look" at its strategy, a top US official told reporters.

- More commandos? -

In the wake of Ramadi's capture, US officials announced that 2,000 AT4 anti-tank weapons were on the way to Iraq to help Iraqi troops counter massive car bombs.

The move was part of an effort to ramp up the arming of Iraqi troops and Sunni tribesmen.

But both at home and abroad Obama's stance has been slammed as overly cautious.

The president faces growing calls for a dramatic overhaul of a campaign which has relied on American-led air power backing up US-equipped local forces.

Some lawmakers urged a major increase in US troops, at least several thousand or more, while former senior officials called for a bolder diplomatic calculus.

Senator John McCain and other voices on the right said Obama should deploy more special forces and stage more raids similar to an operation a week ago in which US commandos killed an IS financier in eastern Syria.

The elite special forces could be "forward deployed" across the battlefront to help call in air strikes, assist Iraqi troops and hunt down jihadist commanders, McCain argued.

"What we desperately need is a comprehensive strategy, the decisive application of an increased but still limited amount of US military power, and a concerted effort by the Iraqi government to recruit, train and equip Sunni forces," McCain said.

Critics also urged Washington to take a more forceful diplomatic stance to prevent the jihadists from taking advantage of divisions inside the international coalition and of the alienation of Sunnis in Iraq.

The US could no longer ignore the civil war in Syria and would have to take bolder action to help "moderate" rebels there, which might persuade Sunni governments to get more involved in the anti-IS fight, analysts said.

"The bottom line remains: the strategy isn't working and it can't work," said Richard Haass, a former senior diplomat.

It was unrealistic to treat Iraq as a single country, as it was irrevocably splintering into three parts -- Kurdish, Sunni and Shiite, said Haass, president of the Council on Foreign Relations.

As a result, Washington would have to channel military aid directly to local forces without working through the dysfunctional central government in Baghdad, he said.

"The time has come to accept that you can't put Humpty Dumpty back together again. The old multiethnic Iraq is over," Haass told Bloomberg television.

- 'Lying by omission' -

The first step in salvaging Washington's strategy was to be honest about the course of the war, said Anthony Cordesman of the Center for Strategic and International Studies.

There were signs this week of some long overdue candor from an administration that has tended "to spin events, downplay risk and problems to the point of lying by omission," Cordesman wrote in a commentary.

For Obama, an outspoken opponent of the 2003 invasion of Iraq and the occupation that followed, an over-arching goal has been to steer clear of another major ground war in the Middle East.

But, Cordesman argued, "it is time the president's White House team learned that losing wars by default and inaction is scarcely a better historical record."