On Tuesday, September 12, Russian defense minister Sergei Shoigu sat with Syrian president Bashar al-Assad in Damascus. According to Russian embassy social-media posts they discussed joint cooperation against Islamic State. This comes on the heels of the Syrian army reaching the city of Deir ez-Zor on the Euphrates River in eastern Syria and breaking a two-and-a-half-year siege. Russia has played a key role in the Syrian army’s successes, which increasingly means that Russian-backed Syrian forces are coming into contact with the U.S.-backed Syrian Democratic Forces (SDF). On September 16th the US-led coalition said a Russian airstrike east of the Euphrates river wounded several members of the SDF. As ISIS declines, its vacuum is filled with groups whose agendas are not the same and, in the case of Washington, whose policy remains unclear in eastern Syria. That is leading to greater Iranian influence across Iraq and Syria, and it leaves U.S. allies in the Gulf, Israel and on the ground in Syria wondering what comes next.

Days after the Syrian army—with aid from the Russian air force—broke the siege of Deir Ez-Zor, the U.S.-backed SDF launched an offensive to reach the city from the other side of the Euphrates River. Kurdish media network Rudawreported that they had reached the city’s industrial zone on September 10. Deir Ez-Zor is strategically significant because it is the largest city of the Deir ez-Zor Governorate that stretches on both sides of the Euphrates River to the Iraqi border. The Islamic State expanded along this area in 2014, using it as a conduit to enter Iraq’s mostly Sunni Anbar province via the crossing at Abu Kamal. As the map of ISIS-controlled areas shrinks by the day, with it’s capital of Raqqa about to be taken by the SDF, the United States, Russia and their allies are eying the next stage of the conflict in Syria and Iraq.

Jonathan Spyer, director of the Rubin Center for Research in International Affairs at the Interdisciplinary Center Herzliya says the current situation raises important questions, especially about Iranian support for the Syrian regime. “We know what the Syrian regime is doing, trying to defeat ISIS and re-assert regime control. The Iranians want the border crossing at Abu Kamal and the land corridor that is part of that,” Spyer says. Control of the crossing and the road helps Iran achieve its goal of linking the Shia militias it backs in Iraq with Hezbollah in Lebanon via its Damascus ally. “We know what the Iranians want, what do the SDF and the Americans want, it is less clear . . . there is no overarching U.S. strategy other than ISIS needing to be destroyed,” he says. Spyer argues that the Iranians see Iraq, Syria and Lebanon as a single space on which they play a masterful strategic game across the region. That is why Hezbollah has been fighting in Syria and its men have been spotted in Iraq. It is why Iraqi militias have served in Syria. The United States by contrast sees each country differently, working with Iraqi prime minister Haider Abadi’s government in Baghdad against ISIS, working with the SDF in Syria, and working with Lebanese Prime Minister Saad Hariri’s government in Beirut. Spyer argues that “turning over management of the Syria file to the Russians” would amount to turning over Syria to America’s adversaries.

Wladimir van Wilgenburg, a Kurdish affair analyst who is in Syria and familiar with the SDF points out that the Russians and Americans have sought to “deconflict” as their forces draw closer. “I don’t think the policies of the SDF is to go through Deir Ez-Zor city, maybe some neighborhoods, but the city is for the regime,” Wilgenburg says. The SDF wants to take the countryside and it appears the Americans are interested in them moving towards the Iraqi border, Wilgenburg says. “I think that is the plan, but they make a line with the Syrian [regime], but the Iranians won’t like it. Russia and Americans will try to coordinate it.” The major question is whether the United States will openly say its policy is to contain Iranian influence and draw attention to the border area as a place to do that.

U.S.-Russia relations in Syria currently work through a “deconfliction” mechanism that has avoided air forces coming into contact. In late August a convoy of several hundred ISIS fighters was allowed to leave the Al-Qalamoun area on the Lebanese-Syrian border under an agreement with Hezbollah. They were supposed to transit to Abu Kamal, because the regime was preparing the Deir Ez-Zor offensive and didn’t want to have to run into the ISIS fighters again. Under pressure from Iraq, which didn’t want the convoy crossing the border, the U.S.-led coalition, targeted a road to prevent the convoy moving on. In a statement the coalition said that it had “communicated to the Russians to deliver a message to the Syrian regime that the coalition will not condone ISIS fighters moving further east to the Iraqi border.” Although coalition air operations crossed the Euphrates River, the coalition continually stresses that it “has no fight with the Syrian regime or its allies in the counter-ISIS fight.”

The Russians seem to be hardening their stance on the U.S. role in Syria. On Sunday, September 10, Russian foreign minister Sergey Lavrov was reported as saying that “anyone who is on Syrian soil or in Syria’s airspace without Damascus’s consent, including the United States, violated international law.” In early September, Sputnik News, which is considered close to the Russian government, reported that “US aircraft evacuates 20 Daesh [ISIS] commanders from Deir ez-Zor –source.” This was obviously misinformation, but it was designed to paint the United States as a bad actor in Syria. On September 11, responding to claims that the United States had struck the Syrian army, the Combined Joint Task Force Operation Inherent Resolve spokesman tweetedthat the rumors were “false, our fight is with ISIS, 22 strikes this week.”

Despite the rumor mongering and quiet war of words, there are also signs that Moscow views the role of the SDF amicably. On September 13 the Russian military was reported to have said that 85 percent of Syria had been liberated from enemies. According to the Associated Press, Lt. Gen Alexander Lapin said 15 percent of the country remained to be retaken. That would indicate that the SDF areas of control, which is around 35 percent of the country, are not seen as controlled by the enemy. Russian military observers have played a role in places like Afrin that are controlled by the SDF but where the United States is not present.

This leaves a major question as to what U.S. policy will be as its allies seek to liberate more areas along the Euphrates River Valley toward the Iraqi border. Currently, the other side of the Iraqi border is controlled mostly by Iranian-backed Shia militias, called the Hashd al-Shaabi, which are officially part of the Iraqi security forces. These forces want to move down and take Al Qa’im across from Abu Kamal. They would then like to link up with the Syrian regime forces and its own Iranian-backed militias. The United States remains committed solely to defeating ISIS, and in Iraq U.S. forces assisting the Iraqis have worked next to the Shia militias in recent campaigns such as Tal Afar. However, in Iraq the coalition’s official policy is not to work with the militias, only the Iraqi army, federal police and other units. This is a convenient bifurcation that is meaningless on the ground, as all these forces are intermingled in the war on ISIS.

What the United States and its SDF allies decide to do in the next months in Syria will likely begin to determine the next stage of the future in the Middle East. If the United States begins to sketch out a policy of containing Iranian influence, then it can do that with its partners. If the United States is only there to defeat ISIS, then its post-ISIS strategy in Iraq and Syria leaves its non-Iranian aligned partners with an unclear future. This has repercussions that stretch beyond the Euphrates River Valley. It affects how Saudi Arabia, the UAE, Israel, the Kurds and Turkey see U.S. commitments and policy.