Raqqa or Deir Ezzor: Where will Islamic States' last stand be?

After seven months of operations aimed at encircling and isolating the city, the morning of Tuesday June 6 marked the beginning of the US-backed Kurdish-led Syrian Democratic Forces' (SDF) assault against Islamic State (ISIS) in Raqqa. An ISIS defeat in the city, coupled with its impending total defeat in Mosul, will doubtlessly be a mortal blow to the group. 

But will their last stand be in their de-facto Syrian capital?

It's no secret that outside of Raqqa province ISIS controls vast swaths of the eastern Syrian province of Deir Ezzor. In the region's provincial capital of the same name where they have besieged a Syrian Army garrison holed up in the airport and surrounding areas for years now. Syrian regime forces, whose manpower is being heavily supplemented by Iranian-backed militias and supported by Russian air power, are advancing eastwards, where their likely aim is to link-up with the isolated garrison and force the militants out. 

As is the case with Raqqa the SDF set up a 1,700-member military council to administer Deir Ezzor in anticipation of a possible operation to rout the militants from that region. 

A successful Raqqa operation for the SDF could cost many fighters and take months. It took the group three months to capture Manbij, which was a relatively peripheral city in ISIS's self-styled caliphate. The SDF hope to incorporate Raqqa into their unrecognized northeast federal region. US officials do not want to see the city returned to the control of the regime following its capture – although they have not endorsed the SDF taking full post-battle control over it. Such incorporation could lead to tensions between the SDF and Damascus. 

Possible tensions over Raqqa's post-ISIS status would pale in comparison to tensions brought on by an SDF advance on, and capture of, Deir Ezzor. A Syrian regime recapture of Deir Ezzor will enable it to link-up with Iranian-backed groups in the Iraqi Shiite-majority Hashd al-Shaabi paramilitaries, which reached the Iraqi border with Syria in the Shingal region on May 29. 

The SDF recently announced they would deny the Iraqi Shiite-majority Hashd al-Shaabi paramilitaries from entering their territories. 

A US seeking to contain, and rollback, a greater Iranian proxy presence in the Middle East is unlikely to welcome such an outcome. 

Forcibly preventing Hashd forces from linking up with allied forces in Syria, however, would entail the US and SDF effectively seizing control over swaths of eastern Syrian border territory and directly challenging the regime there, and possibly increasing the risk of clashing with the regime's Russian backer in the process. 

The Americans have already acknowledged the importance of working with the Russians in any future operation in Deir Ezzor. 

US Major-General Joseph Dunford told a news conference in May that they have already “talked about that [Deir Ezzor] as a specific area that requires” coordination with the Russians. 

“My sense is that the Russians are as enthusiastic as we are to de-conflict operations and ensure that we continue to take the campaign to ISIS and ensure the safety of our personnel,” Dunford said. 

Russia has aircraft and a few thousand troops in Syria which it has used against various groups since intervening in the conflict on the side of the regime in September 2015. The US has special forces in the Kurdish territories of northeast Syria and supports SDF operations with airstrikes from Incirlik Air Base in Turkey, along with other bases and aircraft carriers in the Persian Gulf region. The US presence on the ground in the northeast has reportedly forced Iran to alter the route of its purported corridor from its own territory through Iraq across northern Syria to the Mediterranean Sea. 

Additionally, in the southeast 150 US soldiers and other coalition countries are reportedly based at the Al-Tanf base near the frontiers of Iraq and Jordan. There they have, along with the British, been training Jaysh Maghawir al-Thawra, formerly known as the New Syrian Army (NSyA), anti-ISIS fighters. The group could potentially assist a future SDF assault from the north into Raqqa by assaulting ISIS in Deir Ezzor from the south. 

US warplanes bombed pro-regime forces as they established positions near al-Tanf, one of the “deconfliction zones” in Syria, on two separate occasions: June 6 and May 18. While Russia joined Syria in condemning the May 18 attack it reportedly tried to discourage those forces from establishing positions in that area just before the attack.  

Supporting continued and drawn out regime and militia engagements against various factions across Syria is not in Russia's interests. It wants to bring the conflict to an end through political negotiations now that the regime has the upper hand, following its victory in Aleppo last December, and is no longer at risk of being toppled, as it was shortly before Moscow intervened. ISIS is excluded from all negotiated ceasefires as well as any potential resolution to the conflict and its elimination is something both Moscow and Washington recognize is essential.

The SDF are unlikely to endure more heavy casualties to capture Deir Ezzor, in addition to Raqqa, if they are expected to hand it back to Damascus the day after they do all the dirty work of removing ISIS. Consequently, ISIS's last stand in Syria might be in Deir Ezzor against regime and Shiite militia forces backed by Russian air power with American assent. 

Working with Russia to neutralize the ISIS threat and pressure Damascus to curtail the cross border linking-up of Iranian-backed paramilitary elements will therefore likely prove the most feasible long-term goal for the Americans to pursue in eastern Syria.