President Barack Obama ruled out a shift in strategy in the fight against Islamic State on Monday despite the deadly attacks in Paris, saying putting more US troops on the ground as sought by his political critics "would be a mistake."

Speaking after a G20 summit in Turkey, Obama described the attacks in France that killed 129 people as "a terrible and sickening setback" and vowed to redouble efforts to destroy Islamic State, even as the group threatened to strike Washington.

Mindful of the difficulties that the United States had in controlling Iraq after its invasion in 2003, Obama is very reluctant to commit American ground forces to Middle East conflict zones.

"We are going to continue the strategy that has the best chance of working," he told a news conference, adding that there would be "an intensification" of the effort against Islamic State.

Obama has been criticized for his administration's handling of the current turmoil in Syria and Iraq, with some Republicans calling for a more aggressive approach that would include more US troops on the ground in the region.

Republican presidential candidate Jeb Bush called on Monday for more US troops in leadership positions and as advisers to Iraqi and Kurdish units. He also sought a no-fly zone in Syria, a move Obama has resisted, in part because Islamic State has no air force.

Billionaire businessman Donald Trump, another Republican White House contender, supported sending as many as 10,000 US troops in the region, while South Carolina Senator Lindsey Graham spoke of creating a ground force of US, French and other Nato forces to fight Islamic State.

Obama pushed back against the Republicans and said some were only recommending what the administration had already done against Islamic State while others seemed to think if he were "just more bellicose ... that would make a difference."

"This is not a traditional military opponent. We can retake territory and as long as we keep our troops there we can hold it. But that does not solve the underlying problem of eliminating the dynamics that are producing these kinds of violent, extremist groups," Obama said.

A majority of Americans want the United States to intensify its assault on Islamic State following the Paris attacks, but most remain opposed to sending troops to Iraq or Syria, where the militant group is based, a Reuters/Ipsos poll found.

Obama told reporters that US intelligence agencies had been concerned about a potential attack on the West by Islamic State for more than a year, but he said none of the warnings they had received were specific enough to have prevented Friday's attacks in Paris.

Even so, the United States is streamlining the process by which it shares intelligence and operational military information with France.

Obama criticized as "shameful" the idea that Christian refugees should be given preference by the United States in decisions over admitting people fleeing violence in Syria. – Reuters