The US decision came as Syrian army is gaining upper hand in fighting against militants groups capturing the strategic town of Qusayr last week.

The White House said on Thursday that Washington would provide "direct military support" to the foreign-backed militants but did specify whether it would include lethal aid, which would mark a reversal of Obama's resistance to arming the terrorists.

"The president has made a decision about providing more support to the opposition. That will involve providing direct support to the SMC,” US Deputy National Security Adviser Ben Rhodes said on Thursday, referring to the so-called Syrian Military Council (SMC). “That includes military support," he added.

"I cannot detail for you all of the types of that support, for a variety of reasons, but again, suffice to say this is going to be different in both scope and scale in terms of what we are providing."

Syrian opposition leaders immediately called for anti-aircraft and other sophisticated weaponry. 

Obama has been more cautious than Britain and France, which forced the European Union this month to lift an embargo that had blocked weapons for the militants.

The United States also on Thursday accused Syria of using chemical weapons against the militants, a claim Syria has rejected for several times.

Earlier, a US defense official said the United States would keep F-16 fighter jets and Patriot anti-missile weapons in Jordan -- which borders Syria -- after a joint military exercise ends this month.