By Frank Gardner
Security correspondent, BBC News
The deaths have stirred up anti-US feeling in the region
The apparent raid by US helicopter-borne special forces across the Iraqi-Syrian border - known as an air assault - would have been no impromptu operation.
It would fit into a carefully calibrated step-up in US counter-terrorist operations around the wider Middle East.
In July, President George W Bush reportedly signed an executive order authorising limited incursions by US ground troops into Pakistan's tribal areas, allowing the Pentagon and the CIA - in theory - to go after high value al-Qaeda operatives previously beyond their reach.
In September, an air assault by US special forces targeted the Pakistani village of Angor Adda, resulting in the deaths of about 20 people, all of whom, insist local witnesses, were civilians.
Throughout Monday, US officials refused to confirm or deny that their forces carried out the Syrian raid, but it certainly bears a striking resemblance to what happened in Pakistan the previous month.
Intelligence comes in that a wanted fugitive is operating in the area, the building or compound he is believed to be occupying is identified - and in goes the raid.
Whether or not the mission is successful, the actual effect in both cases has been to stir up local and regional animosity against America and the West.
On Monday, Arabic language internet websites were blazing with angry denunciations of US policy, calling it "a violation by a criminal country," and "a humiliating attack demanding an earth-moving response".
Such is the disgust at Syria's inability to defend its borders that some online contributors are even accusing the Syrian authorities of complicity, suggesting that Washington and Damascus are working together in a "Crusader-Shia alliance" aimed at eradicating Sunni militants.
So far, US counter-terror officials have refused to publicly confirm reports that the intended target was a man named Abu Ghadiya, a senior al-Qaeda leader believed to have been running a network of militants across the border since 2005.
But they say their intelligence suggests a continued, albeit reduced, flow of insurgents across the Syrian border into Iraq.
The number of militants crossing over to attack US and coalition forces is thought to be down from about 150 a month to just 20.
But speaking on condition of anonymity, an official said: "We would not want to see al-Qaeda establish a safe haven in that (Syrian) border area in the way they have in Pakistan".