The commander - a moderate Sunni and an influential rebel leader from Damascus who said he has met intelligence operatives from Western and Arab states - said the US officials were especially keen to obtain information about the identities of Al Nusra insurgents and the locations of their bases.
Then, by the rebel commander's account, the discussion took an unexpected turn.
The Americans began discussing the possibility of drone strikes on Al Nusra camps inside Syria and tried to enlist the rebels to fight their fellow insurgents.
"The US intelligence officer said, 'We can train 30 of your fighters a month, and we want you to fight Al Nusra'," the rebel commander recalled.
Opposition forces should be uniting against Mr Al Assad's more powerful and better-equipped army, not waging war among themselves, the rebel commander replied. The response from a senior US intelligence officer was blunt.
"I'm not going to lie to you. We'd prefer you fight Al Nusra now, and then fight Assad's army. You should kill these Nusra people. We'll do it if you don't," the rebel leader quoted the officer as saying.
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