WASHINGTON: President Barack Obama has signed a secret order authorizing US support for rebels seeking to depose Syrian President Bashar al-Assad and his government, US sources familiar with the matter said.

Obama's order, approved earlier this year and known as an intelligence “finding,” broadly permits the CIA and other US agencies to provide support that could help the rebels oust Assad.

This and other developments signal a shift toward growing, albeit still circumscribed, support for Assad's armed opponents - a shift that intensified following last month's failure of the UN Security Council to agree on tougher sanctions against the Damascus government.

The White House is for now apparently stopping short of giving the rebels lethal weapons, even as some U.S. allies do just that.

But US and European officials have said that there have been noticeable improvements in the coherence and effectiveness of Syrian rebel groups in the past few weeks.

That represents a significant change in assessments of the rebels by Western officials, who previously characterized Assad's opponents as a disorganized, almost chaotic, rabble.

Precisely when Obama signed the secret intelligence authorization, an action not previously reported, could not be determined. The full extent of clandestine support that agencies like the CIA might be providing also is unclear.