Washington (AFP) - Former secretary of state Hillary Clinton blamed the rise of Islamist militants in Iraq and Syria on failures of US policy under President Barack Obama, in an interview published Sunday.

Clinton specifically faulted the US decision to stay on the sidelines of the insurgency against Syria's President Bashar al-Assad as opening the way for the most extreme rebel faction, the Islamic State.

"The failure to help build up a credible fighting force of the people who were the originators of the protests against Assad —- there were Islamists, there were secularists, there was everything in the middle -— the failure to do that left a big vacuum, which the jihadists have now filled," Clinton told the Atlantic.

Clinton, widely considered an undeclared presidential candidate, was an unsuccessful advocate of arming the Syrian rebels when she was secretary of state during Obama's first term.

She was interviewed before the US president's decision Thursday to order limited air strikes to check an IS offensive into Kurdistan, which threatened US nationals and facilities and sent thousands of refugees fleeing into the mountains.

Obama, who oversaw the US withdrawal from Iraq in 2011, vowed not to send US troops back into the country and said Iraqis needed to confront the jihadist threat by forming an inclusive unity government.

Clinton, however, suggested in the interview that Obama lacked a strategy for dealing with the jihadist threat.

"Great nations need organizing principles, and 'Don't do stupid stuff' is not an organizing principle," she said referring to an Obama slogan.

She said the United States must develop an "overarching" strategy to confront Islamist extremism, likening it to the long US struggle against Soviet-led communism.

"One of the reasons why I worry about what's happening in the Middle East right now is because of the breakout capacity of jihadist groups that can affect Europe, can affect the United States," she said. "Jihadist groups are governing territory. They will never stay there, though. They are driven to expand. Their raison d'etre is to be against the West, against the Crusaders, against the fill-in-the-blank—and we all fit into one of these categories.

"How do we try to contain that? I'm thinking a lot about containment, deterrence, and defeat," she said.

Her arguments, seen as an attempt to distance herself from Obama, echoed those of Republican critics who accuse Obama of allowing a power vacuum to develop by failing to bring US leadership to bear in conflicts from Syria to Iraq to Ukraine.