US President Barack Obama has authorised surveillance flights over Syria, two officials said, a move that could pave the way for US airstrikes against Islamic State militant targets.
The White House says Obama has not approved military action inside Syria, but additional intelligence on the Isis militants would probably be required before he could take that step.
Pentagon officials have been drafting options, including airstrikes, for the President.
One official said the Administration needed reliable intelligence from Syria and the surveillance flights were a way of obtaining it.
The New York Times reported the Pentagon would use a combination of aircraft including drones and possibly U2 spy planes with an eye to drafting options to strike militarily near the Iraq-Syria border.
Officials had said the US did not intend to officially notify the Assad Government of the planned flights.
The US began strikes against Isis inside Iraq this month after Obama cited the threat to Americans 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 also go after the group inside neighbouring Syria.
Obama has long resisted taking military action in Syria, as it would plunge the US into a country ravaged by an intractable civil war. But his view appears to have shifted since Isis said 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 said yesterday that Obama has shown 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 yesterday on Obama's decision to authorise 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 National Security Council spokeswoman Caitlin Hayden.
The US stepped up its air surveillance of the Islamic State inside Iraq this year as Obama began considering the prospect of airstrikes there.
And the Administration has run some surveillance missions over Syria, including before an attempted mission to rescue Foley and other US hostages.
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.
Administration officials have said a concern for Obama in seeking to attack Isis inside Syria is the prospect that such a move could unintentionally help embattled Syrian President Bashar al-Assad. Earnest said: "We're not interested in trying to help the Assad regime."
Syria said for the first time that it would work with the international community, including the US, to tackle the Islamist problem.
But Foreign Minister Walid Muallem insisted that any strikes on Syrian territory must be co-ordinated with the Assad Government.
"Syria is ready for co-operation and co-ordination at the regional and international level to fight terrorism," Muallem said in Damascus.
- AP, AFP