A doomed US plan now on hold to train Syrian rebel fighters outside the country to fight ISIS was "nuts," former defence secretary Robert Gates said.
President Barack Obama's administration has suspended its $500 million train and equip effort in the latest embarrassment concerning a Syria strategy that has stumbled from one setback to the next.
Pentagon officials say that instead of training rebel units, the US military would dole out weapons to favored commanders already on the ground.
"I think the idea of training somebody from the outside and sending them in is nuts, it's just not going to work," Gates said in an interview with the Fox News Channel's "Special Report" aired Thursday.
"The only way you can staunch the humanitarian flow, the humanitarian disaster, is through some kind of a safe haven and I think that that's achievable."
Gates, a former CIA director who served as Pentagon chief under both Obama and his Republican predecessor George W. Bush, argued that the US role in the drawn-out Syrian war "should be limited."
"I would not put ground troops in Syria," where a brutal civil war has raged since 2011.
Two small groups of US-trained fighters have crossed into Syria from training centers in Turkey or Jordan this year, but they did not last long.
The first broke up after coming under attack from the Al-Nusra Front, an Al-Qaeda franchise.
The other surrendered much of its equipment, perhaps a quarter of its trucks and guns, to Al-Nusra.
Last month CENTCOM commander General Lloyd Austin admitted that after the debacle only "four or five" Pentagon-trained rebels remain active in Syria.
Gates also said Obama distrusted the military, which was "particularly true in Afghanistan."
"I think there were people in the White House, and I don't want to name any names, who were constantly goading him," Gates said.
When asked if Vice President Joe Biden was one of these people, Gates said, "I think so. And I was told so..."
He said those people were saying "the military is trying to box you in. The military is trying to trap you. The military is trying to bully you. The military is trying to make you do something you don't want to do."