I. Why it Matters

Located in Syria on the Iraqi border and within miles of the Jordanian border, the U.S. garrison at al-Tanf has, since 2016, served as a launching point for counter-ISIS operations and training for Syrian opposition factions fighting the jihadist group. Iranian and Iran-backed forces are deployed in close proximity to the al-Tanf desert outpost, which sits on the strategically significant Baghdad-Damascus highway. U.S. forces in al-Tanf established a 55-km de-confliction zone, beyond which lie an array of forces described as either “pro-regime” or “Iran-backed” that have set up checkpoints in the area. Several incidents in recent months underscore al-Tanf’s potential as a flashpoint between U.S. and Iranian and/or Iran-backed forces.

II. Recent Developments

III. Background

As ISIS’s territorial control in Syria and Iraq shrinks, territories previously held by the group leave a vacuum for conquering parties to further their own influence and agendas. This includes both the U.S., which has been leading a counter-ISIS campaign under the framework of Operation Inherent Resolve, and Iran, which has deployed its own forces and backed non-Iranian militias against ISIS and anti-Assad forces in Syria. The capture and execution by ISIS of an Iranian Revolutionary Guard near al-Tanf in August 2017 confirms an Iranian presence on the ground there, though its extent is difficult to ascertain.

The view from Washington is that Iran’s strategic goal is to establish an east-west land corridor stretching from Iran to Lebanon as a back-up to the existing air corridor that serves as an Iranian arms supply channel to Hizbollah; control of al-Tanf would facilitate this objective.

The view from Tehran is that the U.S. is seeking to develop a north-south corridor in eastern Syria, stretching from the Turkish to the Jordanian border and controlled by Syrian Kurdish parties and other U.S.-backed forces, to curtail Iran’s access to its allies and proxies in the Levant.

IV. Analysis

Limited Response to Douma. On the evening of 7 April 2018, the rebel-held Damascus suburb of Douma was subjected to an apparent chemical weapons attack. Retaliatory military strikes by the U.S. and its Western allies grew increasingly likely after Russia and the P3 - the U.S., the United Kingdom, and France - failed to agree on a mechanism at the Security Council, and were launched against targets in Damascus and Homs in the early hours of 14 April (Syrian time). President Trump declared that "the purpose of our action... is to establish a strong deterrent against the production, spread and use of chemical weapons", while the secretary of defence, Jim Mattis, described the operation as "a one-time shot". By keeping the strikes limited in duration and narrow in purpose, the U.S. and its allies likely wanted to avoid an unintended escalation; Russian officials confirmed that their air defences in Syria were not engaged during the operation. However, President Trump left open the possibility of future action, stating that "the combined American, British and French response to these atrocities will integrate all instruments of our national power: military, economic and diplomatic. We are prepared to sustain this response until the Syrian regime stops its use of prohibited chemical agents". 

The risk is that the presence in close quarters of U.S. and Iranian as well as Iran-backed forces in eastern Syria can lead to an accidental or deliberate clash, in turn raising the risk of direct engagement between Iranian and U.S. forces. Incidents in and around al-Tanf appeared to have ebbed by mid-2017. As one top U.S. official remarked in late August, “the situation [there] is stable. Every – all parties understand, almost … the rules of the game, that’s exactly what we had wanted to be the case”. Yet the October incident underscores the fluid situation and continued potential for clashes between U.S. and pro-Syrian regime forces. In other words, “stability” and “knowing the rules of the game” does not mean that the risks have been entirely eliminated.

A deliberate clash remains unlikely: Iranian/Iran-backed forces probably will not make a direct assault on the garrison but engage in probing operations, while U.S. forces, whose mission is centred on ISIS, are not expected to actively seek out military engagements with pro-Syrian regime forces. The situation could become more volatile once ISIS loses what remains of its territory inside Syria; this will complicate U.S. political and legal justifications for its continued presence at al-Tanf, which at least some officials say is required to blunt Iranian influence and exert leverage on Damascus, while the Syrian regime and its allies over time could seek ways – diplomatic or military – to push for a U.S. withdrawal from the relatively isolated base.

A wildcard factor is ISIS: its fighters, who continue to be present in the area around al-Tanf (even if they do not control territory), may attack either the U.S.-led coalition or Iran-backed forces, raising the possibility of unintended engagement between the other two, if there is misidentification. The 16 November clash highlights ISIS’s ongoing capacity to operate in the al-Tanf area and target U.S. and U.S.-backed forces. Moreover, the anti-ISIS campaign can change operational dynamics and movement along the border regions in the coming months, especially in the context of a race for the spoils.

V. Scenarios and Recommendations

Striking Back? While the U.S.-led strikes on 14 April (Syrian time) were, according to the Pentagon, limited to Syrian chemical facilities, any military action in Syria inevitably presents significant risks of unintended escalation, especially given deepened involvement by several foreign actors. Moscow and Tehran both condemned the operation, with a senior Russian diplomat warning that "such actions will not be left without consequences". If the Syrian government or its backers retaliate, the U.S. and its allies may not be the direct target. The U.S. and its allies are unlikely to be the only or even main targets of retaliation by the Syrian government and its backers. Military action could provoke intensified bombing by the Syrian government and Russia against opposition-held areas. It could also jeopardise local ceasefire arrangements, including the tenuous “de-escalation” in southwestern Syria jointly negotiated by the U.S., Russia, and Jordan. 

A Direct Confrontation Could Occur. Now that ISIS’s territorial control is all but eliminated, attention among most relevant actors will shift more markedly toward means of improving the balance of power on the ground in their favour, so as to strengthen military positioning and negotiating leverage. Iranian forces and their allies might seek to target U.S. forces in and around al-Tanf in retaliation against U.S. actions elsewhere or in an effort to drive the U.S. out of Syria. There is no clear military path to the latter objective, as the U.S. can continue to destroy forces that cross into exclusion zone for the foreseeable future. Yet this could strengthen more hawkish elements in Washington and invite the U.S. to take retaliatory measures of its own, thus starting an escalatory spiral.

To avoid unintended clashes and contain incidents, Russia and the U.S. need to redress the shortcomings of their hotline, to ensure it allows for time-sensitive communication, prevents miscommunication and stops future incidents, such as a breach of the de-confliction zone, from escalating. The shooting down of the Shahed 129 drone in June demonstrated this problem, as Pentagon officials acknowledged that the situation evolved too rapidly to communicate with their Russian counterparts. The communications channel seems to have performed more effectively in the 4 October incident, and again during the 16 November incident with ISIS forces. U.S. and Russian officials should assess whether it is possible to further reduce hotline response times and ensure timely and accurate exchanges of information.

Bracket Al-Tanf: The utility of rebels based at al-Tanf in the anti-ISIS effort has declined, and the U.S. doesn’t currently have any other strategic use for them -- especially because it also has seemingly ended its investment in armed resistance against the Syrian regime. This does marginally decrease U.S. incentive to stay in al-Tanf, but probably not to a point where they are prepared to withdraw unilaterally and cede its control to Iran and its allies. Until the fate of the base is determined in broader negotiations between major parties over Syria’s future or in bilateral arrangements between the U.S. and Russia, Iranian and Iran-backed forces should refrain from breaching the 55-km cordon around the garrison in the air or on the ground.