The Pentagon is to stop building Syrian rebel units to allegedly fight the Takfiri group, ISIL, and focus instead on training and arming vetted leaders, a US defense official said Friday.

The Pentagon is to stop building Syrian rebel units to allegedly fight the Takfiri group, ISIL, and focus instead on training and arming vetted leaders, a US defense official said Friday.

"The model before was we were training infantry-type units. We are now changing to a model that will produce more military combat capability," the official said.

The official declined to say how many leaders would be armed and trained, but noted the new effort would get under way "within days."

The switch in tactics will be seen as a tacit admission that the Pentagon's $500 million program to train thousands of the so-called "moderate" Syrian rebels has failed.

Pentagon spokesman Peter Cook said the training program was only part of the US effort, noting that it has also been arming groups already inside Syria, such as the Kurdish forces defending the border town of Kobane.

"I believe the changes we are instituting today will, over time, increase the combat power of counter-ISIL forces in Syria and ultimately help our campaign achieve a lasting defeat of ISIL," Defense Secretary Ashton Carter said.

Cook said Carter has directed the military "to provide equipment packages and weapons to a select group of vetted leaders and their units so that over time they can make a concerted push into territory still controlled by ISIL."