Is the Pentagon preparing to launch air strikes against ISIS in Syria?

While the White House said Obama has not approved military action inside Syria, additional intelligence on the militants would likely be necessary before he could take that step. Pentagon officials have been drafting potential options for the president, including air strikes.

The US began launching strikes against the Islamic State inside Iraq earlier this month, with Obama citing the threat to American personnel in the country and a humanitarian crisis in the north as his rationale. Top Pentagon officials have said the only way the threat from the militants can be fully eliminated is to go after the group inside neighboring Syria as well.

Obama has long resisted taking military action in Syria, a step that would plunge the US into a country ravaged by an intractable civil war. However, the president's calculus appears to have shifted since the Islamic State announced last week that it had murdered American journalist James Foley, who was held hostage in Syria. The group is also threatening to kill other US citizens being held by the extremists in Syria.

White House spokesman Josh Earnest, on Monday, said that Obama has demonstrated his willingness to order military action when necessary to protect American citizens.

"That is true without regard to international boundaries," he said. The White House would not comment on Obama's decision to authorize surveillance flights over Syria.

"We're not going to comment on intelligence or operational issues, but as we've been saying, we'll use all the tools at our disposal," said Caitlin Hayden, spokeswoman for the White House National Security Council.

The official who confirmed the decision was not authorized to discuss Obama's decision publicly by name, and insisted on anonymity.

The US had already stepped up its air surveillance of the Islamic State inside Iraq earlier this year as Obama began considering the prospect of air strikes there. And the administration has run some surveillance missions over Syria, including ahead of an attempted mission to rescue Foley and other US hostages earlier this summer.

The US special forces who were sent into Syria to carry out the rescue mission did not find the hostages at the location where the military thought they were being held. Officials who confirmed the failed rescue last week said the US was continuing to seek out intelligence on the other hostages' whereabouts.

Administration officials have said a concern for Obama in seeking to take out the Islamic State inside Syria is the prospect that such a move could unintentionally help embattled Syrian President Bashar Assad. The Islamic State is among the group's seeking Assad's ouster, along with rebel forces aided by the US.

The White House on Monday tried to tamp down the notion that action against the Islamic State could bolster the Assad regime, with Earnest saying, "We're not interested in trying to help the Assad regime." However, he acknowledged that "there are a lot of cross pressures here."