The information was revealed during BuzzFeed correspondent Mike Giglio's interview with the commander of one of the rebel groups in the Turkish city of Antakya, near Syrian border.
According to BuzzFeed, it is an "open secret that the commander had once received cash and weapons from the CIA, part of a covert US program that backs rebel groups against both Daesh and the Syrian government of Bashar al-Assad."
When his battalion, like many other US-backed groups, was driven out of Syria by jihadists, he asked Americans to increase their support, which finally proved to be insufficient.
Therefore, he said, he was "out of the game" but now he's received an offer, thanks to which he can return to the battlefield. He was being recruited to work for Russia, Washington's chief rival in Syria, according to Giglio.
"They told me, 'We will support you forever. We won't leave you on your own like your old friends did,' he said. Honestly, I'm still thinking about it," Giglio quoted the commander as saying.
His revelations were confirmed by four other people who Moscow contacted through their intermediaries, Giglio said.
In exchange for assistance, Russia wants the rebels to fight Islamists from Daesh and the Nusra Front. When the extremists are destroyed, the commanders of those rebel battalions who decided to support Moscow will start negotiations with Damascus to end the conflict, and then decide the fate of President Assad, according to Giglio.
"This plan — whatever its chances of succeeding — represents an ideal outcome for Russia in Syria, preserving its influence in a country it considers an important client state while dividing the rebels and helping the regime to a military victory," he said.
Meanwhile, some rebels associated with the United States confirmed in interviews with BuzzFeed that Russia had tried to recruit them, but that they refused the offer.
In contrast, "other rebel leaders were receptive at least to hearing the Russians out," Giglio said, referring to Mousa Humaidi, a 40-year-old ex-businessman from northern Syria, who was a senior leader with the Syrian Revolutionaries Front, or SRF.
"Honestly I found that they are honest and good friends, because they support their friends. Russia has more honor than America," Giglio quoted Humaidi as saying.
The commander interviewed by Giglio in Antakya said that he understands that joining forces with Russia will mean the recognition that Assad's government forces have won. He also said that he fears potential retaliation from the CIA and Turkish authorities.
On the other hand, he said that Moscow, unlike Washington, at least offers a way out. "The Americans just want to buy time. But the Russians are here to work," he said, adding that he still "cannot decide" on the offer because "it's like walking down a dark tunnel, and you don't know if you will find the light."
The journalist's story hasn't been verified by the Russian Foreign Ministry, and it raises some questions. The interview was conducted in Antakya, which neighbors the militant-held Syrian province of Idlib, where government troops fought the Nusra Front with Russian air support.Syrian government allies?
Syria has been mired in civil war since 2011, with government forces loyal to Syrian President Bashar Assad fighting numerous opposition factions and extremist groups.
A US-Russia-brokered ceasefire came into force across Syria on February 27, but it does not apply to terrorist organizations active in the country, such as Daesh and the Nusra Front, which are outlawed in many countries, including Russia.
Despite the ceasefire agreement, violence has escalated in Syria in recent weeks, especially in the northern Aleppo region.