A showdown could be looming between the US, Iran, and the Assad regime at the Syria-Iraq border
In April, Syrian rebel fighters and their US special-forces trainers repulsed an ISIS attack in an hours-long battle marked by suicide bombers and coalition airstrikes.
The battle took place at al Tanf near the Syria-Iraq border, and the camp there is still used by US and UK personnel to train Western-backed fighters.
But with ISIS' territorial presence in Syria continuing to erode, al Tanf and the area around it - near the intersection of the Syrian, Iraqi, and Jordanian borders - looks to be the site of a potential clash between the US-led coalition, its local partners, and the Assad regime and its partners, backed by Iran.
With US-backed forces gearing up to liberate ISIS' self-proclaimed capital in Raqqa and ISIS losing ground elsewhere in the Syria, combatants in the country are reportedly trying to position themselves to assume control of territory vacated by terrorist group.
Recent events in Syria indicate that the Assad "regime and its allies [are] racing to establish an east-west 'Shiite axis' from Iran to Lebanon and the United States [is] seemingly looking to cement a north-south 'Sunni axis' from the Gulf states and Jordan to Turkey," Fabrice Balanche, a French expert on Syria and a visiting fellow at The Washington institute for Near East Policy, wrote recently.
"What's left of Islamic State territory is the key part of Iran's plan to connect Iran to Lebanon," Firas Abi-Ali, senior Middle East analyst at IHS Country Risk in London, told Bloomberg.
Though the battle for Raqqa in northeast Syria, and the balance of power it will create, is far from settled, control there looks set to devolve to Kurdish forces - who are allied with the US and have said they're willing to negotiate with Assad, and by extension Iran, for autonomy.
That could make it more possible for the al Tanf area in southeastern Syria to become a flashpoint in the geopolitical struggle between Iran and its partners, largely Shiite but also including Russia, and the US and its partners in Saudi Arabia and the Gulf Arab states, largely Sunni.
According to Balanche, from al Tanf in southern Syria to Sinjar in Iraq - where Iraqi Shiite paramilitaries recently recaptured ISIS-held territory - "the area is now being contested by various belligerents on behalf of their regional sponsors."
Clashes between the US-led coalition and Syrian forces have already occurred in southeast Syria.
On May 18, coalition airstrikes hit pro-regime forces "that were advancing well inside an established de-confliction zone" northeast of al Tanf, US Central Command said in a release.
"This action was taken after apparent Russian attempts to dissuade Syrian pro-regime movement south towards At Tanf were unsuccessful," the release said. The strike was a limited engagement and not part of a new strategy, US Defense Department spokesman Eric Pahon told Bloomberg.
Intelligence sources have told Reuters that the coalition's presence near al Tanf is meant to keep Iranian-backed forces from securing an overland route between Syria and Iraq.
More recently, Western-backed Syrian rebels said Russian jets had bombed them to stop their push to capture a checkpoint on the Damascus-Baghdad highway near the Syrian borders with Iraq and Jordan.
While the Syrian regime and its associates may not have the capabilities to take on US forces and partners at al Tanf, their goal may be to surround the position and render it useless, Balanche told Military Times.
Washington's long-term strategy for the region, and how it would deal with a potential conflict between its partners and Iranian-backed forces, remains unclear.
While US officials have said the US focus continues to be on defeating ISIS, airstrikes on Syrian forces launched earlier this year President Donald Trump were a more direct challenge to Assad than that taken by Obama.
Trump's recent exhortations to Gulf Arab states to "stand united" against Iran, as well as his past bellicosity toward Tehran, suggest that his administration could pursue a more aggressive Middle East policy going forward.
However, Saudi Arabia and the United Arab Emirates, possibly emboldened by Trump's rhetoric, have released public broadsides against Gulf Cooperation Council partner Qatar, opening a rift that could shake up the anti-Iran front the GCC has thus far presented.
"The GCC could harm it own interests in this fight and is at risk of becoming more vulnerable to Iranian encroachment," a Western diplomat based in Doha told Reuters.
Turmoil in the Gulf notwithstanding, US willingness or ability to check Iranian regional ambitions is far from certain.
"There's not much the US can do about Iran in Syria," Cliff Kupchan, chairman of New York-based risk-consultant Eurasia Group, told Bloomberg. "Iran is closer, and cares more."