During a US Senate hearing on Wednesday, US Defense Secretary Ash Carter said that a US program aimed at training moderate rebels to fight against the "Islamic State" has only yielded 60 Syrian fighters.

"The number is much smaller than we hoped for at this point," Carter said, addressing US Senator John McCain, who chairs Congress' Armed Services Committee.

McCain, an avid critic of US President Barack Obama's foreign policy, told Carter that the figure was a cause of concern.

"I got to tell you that after four years, Mr. Secretary, that is not a very impressive number," McCain said in response to Carter's statement and referring to the time passed since the Syrian conflict began.

McCain added that the US government's "means" and "current level of effort are not aligned."

"That suggests we are not winning, and when you are not winning in war, you are losing," McCain told Carter.

But the defense secretary backed Obama's policy, while adding that more needed to be done in order to strengthen the program aimed at training local forces.

"We are looking for ways to streamline our train and equip program's vetting process to get more troops into the training pipeline," Carter told Congress, referring to the rigorous vetting procedures to accept a fighter into the program.

"We are also refining our curriculum, expanding our outreach to the moderate opposition, and incorporating lessons learned from the first training class," Carter added.

While the program was initially proposed to train moderate Syrian fighters to combat forces loyal to Syrian President Bashar al-Assad, its focus shifted after the rise of the Islamic State, which gained notoriety last year after taking control of Mosul, Iraq's second-largest city.

Carter's statements come amid a surge in US military operations against Islamic State targets, most notably the bombardment of the militant group's de facto capital, Raqqa, in Syria.

The self-proclaimed Islamic State has taken over large swathes of land in Syria and Iraq due to the security vacuum following the US withdrawal of security forces from Iraq in 2011 and the uprising-turned-conflict that emerged in Syria the same year.

ls/kms (AP, Reuters)