(CNN) Russia and the regime of Syrian President Bashar al-Assad are attempting to entice US-backed rebels based at the At Tanf garrison in southern Syria to switch sides, US officials tell CNN, in an apparent bid to oust the coalition from a strategic piece of real estate that is seen as crucial to Syria and Iran's long-term interests in the region.
It's just the latest gambit in a months-long tug of war between the US and Assad and his Russian and Iranian backers in the Syrian desert.
One official said the recruitment campaign, which appears to have had very limited, if any, success to date, is aimed at mid-level commanders of the groups being trained and equipped by the US-led coalition at the At Tanf base which sits in near the tri-border area of Syria, Jordan and Iraq.
So far, the coalition says there has only been "less than a handful" of defections from the US-backed Maghawir al-Thawra group, one of the larger units based at At Tanf.
US Army Col. Ryan Dillon, a coalition spokesman, told CNN that one of the defectors was actively attempting to recruit his former comrades and convince them to join the regime but added that those efforts were having no measurable success to date. Dillon would not say whether Russia or the regime were directly behind the recruiting effort.
The official told CNN that the leader of the recruitment effort is a former rebel sub-commander who has criticized the US forces at At Tanf and has promised would-be recruits positions in the regime's armed forces as they clear their homelands in the Middle Euphrates River Valley. This has has prompted the US military to be concerned about more defections in the future given that the regime has blocked the coalition and its allies from advancing on that same area.
He added the regime's recruitment effort was assessed to have two objectives, building a force of local fighters and driving the coalition out of key real-estate in southern Syria.
The first objective is fulfilling the regime's need for a "hold-force" of Sunni Arabs capable of securing areas the regime captures from ISIS.
US officials have said some 80% of the regime's effective fighters are Iranian-backed Shia militias and the pro-regime forces near At Tanf consist primarily of Iranian-backed Shia groups. The coalition has said publicly that many of its allied fighters at At Tanf hail from the Middle Euphrates River Valley, a key ISIS-held area where US officials believe the terror group has relocated its leadership and based some 5,000 to 10,000 fighters.
The second objective involves an attempt to weaken the coalition's rationale for occupying At Tanf, allowing Moscow, Damascus and Tehran to pressure the US and its allies to leave the strategically valuable area.
By poaching leaders of the rebel group, the regime and its Russian and Iranian allies would be able to better pressure the US and coalition troops to vacate the strategic tri-border area near At Tanf, a US official familiar with the development told CNN.
"Assad and his allies realize that the best way to undermine the coalition campaign in Syria is to target the local Syrian partners that the coalition is working by, with, and through," Nick Heras, a fellow at the Center for New American Security who focuses on Middle Eastern security, told CNN.
"Some of the Syrian fighters at the Tanf garrison have decided to cut the best deal with Assad now, and be part of his armies, rather than to fight with the Americans, be labeled as 'traitors,' by the regime, and then have to deal with Assad's wrath." Heras added.
The prospect of Russia using such rationale to eject the US from Syria was raised last month by the head of US Special Operations Command, Gen. Raymond "Tony" Thomas.
"Here's the conundrum, we are operating in the sovereign country of Syria," Thomas told an audience at the Aspen Security Forum while adding that Russia could potentially use legal mechanisms to seek the ouster of the US.
CNN has previously reported that pro-regime forces had established a number of outposts and checkpoints in the area just outside the 55 kilometer "de-confliction" zone surrounding At Tanf, which was negotiated by Russia and the US-led coalition.
US officials have told CNN they believe pro-regime militias backed by Iran are setting up a series of checkpoints as part of an effort to establish a strategic overland route from Iran to the Mediterranean coast.
That proximity led to some clashes in June, including US airstrikes against regime forces who had encroached on the zone and US jets shooting down two pro-regime drones that were perceived to pose a threat to local allies and their coalition advisers.
But US officials have said repeatedly that tensions between the coalition and regime forces had abated in the intervening weeks
"We have actually come to a number of arrangements, you know, drawing a line on the ground of where certain forces should be and that has held extremely well," the US special envoy for the fight against ISIS, Brett McGurk, told CNN's Michelle Kosinski Wednesday.
But while the Pentagon and State Department have noted reduced tensions, a US defense official told CNN Wednesday that the hundreds of pro-regime troops had begun reinforcing outside the de-confliction zone, bringing in trucks, artillery, anti-aircraft guns and additional fighters to bolster their positions.
News of the Russian/Regime recruitment effort was presented to coalition military advisers by representatives of the Maghawir al-Thawra group.
But coalition officials say only a very small "handful" of Maghawir al-Thawra fighters have defected from the coalition's counter-ISIS effort.
"We can confirm there have been a handful of isolated defections," US Army Col. Joe Scrocca told CNN Tuesday, while adding that "the Maghawir al-Thawra has been a trusted partner in the counter-ISIS campaign and we will continue to support their efforts to defeat ISIS in Syria."
Dillon told CNN Wednesday that the leadership of Maghawir al-Thawra remained at At Tanf.
But any additional reduction of fighters is likely to be of concern to the coalition following the recent departure of an entire coalition-backed rebel unit.
Last week, CNN was the first to report that a US-backed rebel group, Shohada Al Quartyan, had balked at the coalition's insistence that it only fight ISIS and not the regime of Bashar Al Assad, opting to leave At Tanf and conduct independent operations against the regime.
The group's decision to fight Assad's troops prompted the coalition to end its support for Shohada Al Quartyan, the first time the coalition has ended its support for a vetted Syrian opposition group, US Dillon told reporters last week.
While negotiations had been ongoing with Shohada Al Quartyan, with US advisers meeting with the group's leadership Monday to explore whether the group could return to the coalition effort, Scrocca told CNN that the coalition stood by its decision to cease its support.
Scrocca described the meeting as "cordial" saying that they had "negotiated to get many of the heavy weapons and other equipment back."
"They also agreed not to conduct offensive operations against the Syrian Regime from inside the 55km de-confliction zone," Scrocca said but added that while they had been an important partner in the fight against ISIS, "We are no longer supporting the (Shohada Al Quartyan)."
"The coalition will continue to train, advise, assist, and accompany other vetted partner forces in southern Syria that wish to defeat ISIS above other objectives," he added.
US and coalition officials told CNN that the group had indeed turned in some of its equipment, including heavy machine guns, though the officials said that the group had retained sufficient small arms and vehicles to carry out independent operations against Assad's forces.
While the group has not been forced to leave the de-confliction zone, the coalition has prohibited its fighters from carrying out offensives against the regime from within the zone.
McGurk told CNN that the group was cut off because its desire to fight the regime put US forces at risk.
"A Syrian group that we might work with wants to basically use the protection of living with us to go out and conduct attacks against the regime and then come back and live in close proximity to US personnel, that's completely unacceptable, because it puts US personnel at risk," McGurk said.
"So there are rules of the road for groups that we work with and that was one very minor incident, but, you know, it's one -- it's an incident that we handled," he added.