Senators in Washington have criticised the US military's apparent failure to train moderate Syrian rebels to counter the Islamic State of Iraq and the Levant (ISIL) group and other opposition factions in Syria.
Only a handful of the estimated 60 deployed US-trained Syrian fighters are still engaged in the campaign, which is substantially short of the US goal to train and equip 5,400 a year at a cost of $500m.
Lloyd Austin, a top US general who oversees the war effort in Syria, told the Senate Armed Services Committee on Wednesday that "four or five" US-trained fighters remained on the battlefield.
Austin's admission came as defence officials scrambled separately to respond to allegations that they skewed intelligence assessments to exaggerate the progress made against ISIL.
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He said he would take "appropriate actions" if an investigation by the defence department's inspector general finds that senior defence officials altered intelligence.
After the first 54 rebels - part of the Division 30 group - were sent to fight in Aleppo province in July, they were trounced by the Nusra Front, a Syrian armed group that viewed Division 30 as an enemy due to their affiliation with the US military - which has launched many air strikes against the Nusra Front.
The Nusra Front killed several of the fighters and took others hostage while many fled.
In August, Division 30 accused the US military of misrepresenting its mission, saying it signed up to fight ISIL, not Nusra Front.
At Wednesday's hearing, John McCain, chairman of Senate Armed Services Committee, called the US bid a failure, outlined his vision of a US strategy to fight ISIL and suggested that more US troops might eventually be needed.
"We need to help establish safe zones inside Syria where refugees and displaced people can be secure," he said.
"We need forward air controllers to add precision and lethality to our air campaign. While no one believes that we need to invade Iraq or Syria, the fact is that we will likely need additional US special forces and military advisers to be successful."
US not 'serious'
Marwan Kabalan, a political analyst, told Al Jazeera that most people "do not believe" that US efforts to arm the Syrian opposition have been "serious or genuine".
"After years of talking about arming the Syrian opposition, they only sent about 60," he said.
Pointing to the US proposal to train 5,400 fighters - a figure many consider too small to make a real impact on the conflict - Kabalan said: "They are probably trying to provide the impression that they are trying to do something in Syria.
"They are trying to please their Gulf Arab allies and they are trying to gain their support for the Iran nuclear deal."
Source: Al Jazeera and agencies