The Pentagon says it is halting its troubled program to build Syrian rebel units to fight the Islamic State and focus instead on training and arming vetted leaders already on the ground.
"The model before was we were training infantry-type units. We are now changing to a model that will produce more military combat capability," a senior US defence official said on Friday (local time).
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 US$500 million ($A688.80 million) program to train thousands of "moderate" Syrian rebels has failed.
Two small groups of US-trained fighters have crossed into Syria from Turkey this year, but one broke up after coming under attack and the other surrendered much of its equipment to an al-Qaeda front group.
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."
Speaking at a news conference in London, Carter admitted he had been dissatisfied with the previous training program, and said: "We have devised a number of different approaches."
In January, President Barack Obama's administration unveiled the US$500-million program to train up to 15,000 vetted Syrian rebels in neighbouring countries.