On July 29, al Qaeda-affiliated Nusra Front captured many of the 54 graduates of the $500 million US training program as soon as they entered Syria.
Rebels believe the plans were leaked because Turkish officials feared that the US-trained Syrians would one day attack Islamist fighters that Turkey is close to, including Nusra and another major Islamist force, Ahrar al Sham, McClatchy reported.
"Only the Americans and the Turks knew" about the plans for the train-and-equip fighters to enter Syria, said an officer of one rebel group. "We have sources who tell us the Turks warned Nusra that they would be targeted by this group."
The Syrian rebel officer said Nusra still holds 22 of his comrades in Azzaz, a Syrian town just south of the Turkish border.
"Right now the only thing keeping our men alive is that Turkey does not want them executed – al Qaeda always executes Arabs who work for the CIA," he said.
As for Washington, Pentagon spokesman Navy Captain Jeff Davis said the US military had seen "no indications that Turkish officials alerted the Nusra Front to the movements" of the US-trained forces.
Other anonymous Turkish officials "acknowledged the likely accuracy of the claims," McClatchy reported.
One official said the plans were leaked in hopes the failure of the train-and-equip program would lead the Americans to invest in the training and arming of rebel groups aimed at toppling Syrian President Bashar Assad.
Another rebel commander told McClatchy he was not surprised that Nusra would target the US-trained fighters, saying the ideologies of Nusra and Ahrar al Sham are similar to that of the Islamic State.
"Nusra are al Qaeda by their own admission," said the commander. "And there's no ideological difference between [Islamic State] and the Nusra Front, just a political fight for control. All of the top Nusra commanders were once in the Islamic State."
The United States and Turkey have clashed over what US officials view as Turkey's willingness to work with Nusra, which the United States labeled a terrorist organization three years ago.
Turkey, meanwhile, has criticized the train-and-equip program for its insistence that participants agree to focus their efforts on defeating the Islamic State, not on battling Assad, McClatchy reported.