By helping Assad's forces bridge the river, Moscow is increasing the risk of direct confrontation while obstructing U.S. efforts to defeat IS, stabilize eastern Syria, and limit Iranian arms transfers.
The Russian Ministry of Defense announced today that "Syrian government troops" crossed to the east bank of the Euphrates River using a Russian pontoon bridge and amphibious vehicles. Although the situation remains fluid, the crossing by what appeared to be elements of Syria's Iranian-trained and Russian-supported "5th Corps" has deep implications for U.S. policy on the Islamic State (IS), the Syria war, and Iran.
First, the move significantly discredits the argument that the Euphrates can serve as a viable deconfliction line while IS implodes, much like the Elbe River separated Russian and American forces in Europe at the conclusion of World War II. The U.S.-backed Syrian Democratic Forces are arriving at Deir al-Zour from the northeast while Russian-supported Syrian forces and Shia militias (including Hezbollah) are arriving from the west. According to Russian media, the contingent crossing the Euphrates is a collection of local and national regime forces called the 5th Corps, many of whose members have been trained and organized by Iran's Islamic Revolutionary Guard Corps (IRGC) and Russia. The crossing increases the likelihood of confrontation between proxies or even between U.S. and Russian forces, as highlighted on September 16 when Russian aviation reportedly bombed SDF targets located within a couple miles of U.S. Special Operations Forces. This raises the question of how the United States intends to protect the SDF and other proxies fighting IS.
The move also complicates any potential SDF push down the east bank of the Euphrates toward local oil and gas fields, which could be used to fund reconstruction in former IS-controlled areas. Syrian regime spokeswoman Bouthaina Shaaban told Iran's Press TV that Bashar al-Assad's "strategic intent" was to halt the SDF's advance, describing the joint Kurdish-Arab brigade as an illegitimate aggressor and equating it with IS. If Russian and pro-Assad forces hold the bridgehead on the east bank, they will likely block the primary north-south road on that side of the river, forcing the SDF to continue pushing down the IS-controlled Khabur River Valley in order to reach the oil fields further south.
Assuming they are unable to capture the major energy and agricultural zones south of Deir al-Zour, the SDF -- and Washington -- would lose much of their leverage over the Assad regime, Iran, and Russia in any political settlement to the Syria crisis. That scenario might also further Assad's plan to retake "every inch" of the country by military means. In light of the regime's depleted manpower, that approach would likely entail wider involvement by the IRGC and Shia militias from Iraq, Afghanistan, and beyond. Given the large Sunni Arab majority population in the Euphrates Valley, such an outcome would exacerbate sectarian and extremist violence in the area, resulting in a "New Syria" that refugees are unlikely to return to.
In addition, the crossing brings Iran one step closer to its stated goal of creating a land bridge between Iraq and Syria, giving the Islamic Republic another avenue through which to place troops and weapons on the borders of U.S. allies. Tehran has steadily worked toward that goal even as Israel reached a de-escalation agreement in southwestern Syria designed to keep Hezbollah and other Iranian-supported militias a few kilometers away from the Golan Heights frontier. Such developments have incensed Israel's security establishment, increasing the likelihood that they will expand their military operations in and around Syria to loosen Iran's deepening grip on the country.
To head off this growing list of problems, the United States is engaging in serious diplomacy and communication with Moscow to avoid further military complications. Yet Washington also needs to reemphasize its support for the SDF at a time when the lines of control between them and pro-Assad forces are narrowing. This means establishing clear policy on what the United States will and will not do to defend its proxies in eastern Syria and elsewhere. In June, U.S. forces struck Shia militias threatening al-Tanf base in southern Syria, then downed an Assad regime aircraft attacking the SDF; these incidents serve as models for how to support proxies while avoiding escalation.
Washington's primary objective is to defeat IS, but the administration has also stated its intent to contain Iran's "malign activity" in the region. Russian diplomats claim there is no military solution to the conflict, but today's Euphrates crossing shows that defense officials in Moscow and Tehran have something different in mind, raising the risk of direct U.S. confrontation with Assad, Iran, and Russia. If one purpose of U.S. support for local actors such as the SDF is "shaping the environment" to contain Iran and its allies, then Washington needs to recognize that Tehran and Assad are directly challenging this goal with the help of Russian airpower. U.S. officials therefore need to decide what diplomatic and military moves are necessary, including frank conversations with the Russians.
Andrew J. Tabler is the Martin J. Gross Fellow in The Washington Institute's Program on Arab Politics.