US President Barack Obama calls the Islamic State a jihadist "cancer" threatening the Middle East and the rest of the world but has so far backed only limited air strikes against the extremists.
If the United States intends to decisively defeat IS, what diplomatic and military means would be needed to crush them?
Experts say Obama would have to dramatically expand US bombing raids in both Iraq and Syria, rally Western and Arab allies to the cause and heavily arm local forces fighting the jihadists.
What military action would be needed?
The United States would have to launch a major air war against IS forces in both Iraq and Syria while relying on the Baghdad government, as well as Kurdish and Sunni tribes to fight the extremists on the ground, former commanders said.
The US military has carried out dozens of bombing raids over the past weeks in Iraq. But to dismantle IS, the Americans would have to unleash the full might of their air power, which likely would involve hundreds of aircraft and hundreds of bombing runs a day.
"Air power needs to be applied like a thunderstorm, not a drizzle," said Dave Deptula, a retired US Air Force lieutenant general who helped plan and oversee air operations in Afghanistan and the Iraq.
The model for such an approach is the 2001 war in Afghanistan that toppled the Taliban regime, as American warplanes rolled back militants in bombing raids and the Northern Alliance moved in on the ground, said Deptula, dean of the Mitchell Institute for Aerospace Studies.
Some analysts suggested that Washington will need to deploy more special operations forces to direct sensitive air strikes.
But Deptula said hi-tech aircraft can find their targets without help from ground troops.
"You don't need any boots on the ground," he told AFP.
Even the most strident hawks are not calling for sending in ground forces in large numbers. Instead, there are calls for expanding the arming and equipping of local forces in both Iraq and Syria.
Deputy national security advisor Ben Rhodes said "the long-term strategy is going to have to involve people on the ground taking the fight to ISIL" (IS), citing Iraqi, Kurdish and Syrian fighters.
Can IS be defeated without military action in Syria?
The answer is "no", according to America's top-ranking officer, General Martin Dempsey, and a host of experts and analysts.
IS cannot be allowed to use Syria as a sanctuary, Dempsey said.
And some analysts and ex-military officers said Washington could invoke the right to "self-defence" under international law to carry out unilateral attacks on IS in Syria, given that Damascus has lost control over parts of its territory.
But the United States would have to alter its cautious approach to the Syrian civil war, and funnel more arms and aid to Sunnis who reject both President Bashar al-Assad's regime and the IS extremists.
Such an approach could lead Washington into a rapprochement with the Damascus regime, some critics say, but US officials insist that is not in the cards.
What diplomatic strategy would be required?
The United States would have to form an unlikely coalition of traditional allies in Europe and rival powers in the Middle East, including Iran and Saudi Arabia, analysts say. That could require forging discreet accommodation with its foes in Tehran, who share the goal of defeating the IS jihadists.
To convey US resolve, Obama would have to openly declare that Washington's goal is to defeat IS, said Zalmay Khalilzad, the former US ambassador to Afghanistan and Iraq.
"The United States could galvanize even more international action by publicly declaring that its objective is to defeat IS," he wrote in The National Interest magazine.
For war-weary Americans, Obama would have to lay out the case for action and explain why the extremists pose a direct danger to the United States.
Washington also would need to press Turkey to close its border to Syria to deprive IS forces of foreign volunteers and lend more aid to Jordan and other states inundated with refugees, analysts say.
What role would Sunnis play?
Iraq's Sunni population was stigmatized under Baghdad's Shiite-led government over the past eight years, providing fertile ground for the IS extremists.
Washington hopes a new government under Haidar al-Abadi will reach out to the alienated Sunni community. And US officials will push Baghdad to reform its army, which "essentially had become sectarian and abusive", said Anthony Cordesman of the Center for Strategic and International Studies.
But it remains unclear if the Baghdad government and the West can win over Sunni tribal leaders and persuade them to take on IS extremists.