With the fall of the Islamic State group's last significant stronghold in Syria, Iranian and Russian-backed Syrian troops now turn to face off with their main rival, the U.S.-backed forces holding large oil fields and strategic territory in the country's north and east.
The complicated map puts U.S. and Iranian forces at close proximity, standing just across the Euphrates River from each other, amid multiple hotspots that could turn violent, particularly in the absence of a clear American policy.
There are already signs.
Iran threatened last week that Syrian troops will advance toward Raqqa, the former IS capital, which fell to the U.S.-backed Syrian Democratic Forces in October, raising the potential for a clash there. The Kurdish-led SDF also controls some of Syria's largest oil fields, in the oil-rich eastern Deir el-Zour province, an essential resource that the Syrian government also says it will take back.
The SDF also faces restlessness in an Arab-majority town it liberated last year, a possible sign of things to come in other areas that the Kurdish-dominated forces control in their self-rule area in northern Syria, now about 25 percent of the country's territory.
The question now is whether the United States is willing to confront the troops of Syrian President Bashar al-Assad and Iranian-backed militiamen. The Kurds are seeking a clear American commitment to help them defend their gains. American officials have said little of their plans and objectives in Syria beyond general statements about continuing to deny IS safe havens and continuing to train and equip allies.
Syria, U.S., Russia plans
During a meeting this week with Ali Akbar Velayati, the adviser of Iran's supreme leader, Assad said his war was against terrorism and against plans to partition Syria, a direct reference to Kurdish aspirations for a recognized autonomous zone in the north. He repeated that his government plans to regain control of all of Syria.
Government victories "have foiled all partition plans and the goals of terrorism and the countries sponsoring it," Assad said.
Meanwhile, four U.S. officials said Thursday the U.S. and Russia are nearing an agreement on Syria for how they hope to resolve the Arab country's civil war once IS is defeated. If clinched, the deal could be announced by President Donald Trump and Russian President Vladimir Putin after a meeting in Vietnam on Friday, they said.
The United States has been reluctant to hold a formal meeting between the leaders unless they have a substantive agreement to announce. The officials weren't authorized to discuss the deliberations and requested anonymity.
With its collapse in Boukamal on Thursday, the Islamic State group has no major territory left in Syria or Iraq. Its militants are believed to have pulled back into the desert, east and west of the Euphrates River. The group has a small presence near the capital, Damascus. Late Thursday, the extremist group carried out a counteroffensive in Boukamal, regaining control of more than 40 percent of the border town.
The Euphrates now stands as the dividing line between Syrian government troops and the SDF in much of Deir el-Zour province.
Government forces and their allies, including Iranian troops and fighters from the Lebanese militant group Hezbollah, control the western bank. They hold the provincial capital and several small oil fields.
The Kurdish-led force, along with American troops advising them, is on the eastern bank. They hold two of Syria's largest oil fields, nearly a dozen smaller ones, one of the largest gas fields and large parts of the border with Iraq. They say they are determined to keep the government from crossing the river.
Iran's Velayati said the U.S. presence aims to divide Syria. "They have not and will not succeed in Iraq and they will also not succeed in Syria," he said during a visit to Lebanon last weekend. "We will soon see the Syrian government and popular forces in Syria east of the Euphrates and they will liberate the city of Raqqa."
The U.S. coalition declined to comment on Velayati's remarks, saying "it would not be appropriate to comment on speculation or rumor by any third party."
Washington has been wary of Iran's increasing influence in the area and its attempts to establish a land corridor from Iran across Iraq and Syria to Lebanon. For weeks, the coalition said the SDF intended to push to Boukamal. Now it is not clear what the U.S. will do.
To avoid frictions in the crowded battlefield, the U.S.-led coalition said it maintains contacts with Assad's ally Russia.
Defense Secretary Jim Mattis acknowledged this week that allies have pressed for a clearer U.S. policy in Syria. The priority was to get the U.N.-sponsored peace talks back on track, he said, offering few details.
"We're trying to get this into the diplomatic mode so we can get things sorted out ... and make certain [that] minorities — whoever they are — are not just subject to more of what we've seen" under Assad, he said, apparently referring to ensuring some sort of accommodation to Kurdish ambitions.
The talks, scheduled for Nov. 28, have already been challenged by Russia, which seeks a bigger role. Moscow called for intra-Syrian talks to chart a political process and invited the dominant Kurdish party that forms the backbone of the SDF, the first such international invitation. A date for the Russia talks has not been set.
Yezid Sayigh, a senior fellow at the Carnegie Middle East Center in Beirut, predicted the Syrian government will use military pressure to reach a negotiated solution with the Kurds amid lack of evidence that the U.S. has any "commitment to engineering political change in Syria or indeed has a Syria policy at all." In an article last week in the Al-Hayat newspaper, Sayigh said Russia is the likely arbiter between Kurds and the government.
Ilham Ahmed, a senior politician with the political arm of the SDF, said indirect talks with the government have taken place but there are no signs of a change in their position.
"A clear position from the coalition can prevent confrontation," she said.
Ahmed denied reports that the government demanded the Kurds return Arab-majority lands that SDF control, which include Raqqa. She recognized oil fields can be a major bargaining chip.
"The oil fields play two opposite roles. They can be an effective way to negotiations. But they can also be the cause for a new war if they reject the solution," Ahmed said.
More than half of Syria's oil wealth is based in Deir el-Zour. Syria had proven oil reserves of 2.5 billion barrels, and the industry was a pillar of the Syrian economy before the conflict in 2011.
Meanwhile, the Kurdish-led SDF faces the complications of trying to run Arab-dominated areas. With U.S.-backing, the force sought to allay any Arab residents' fears of Kurdish domination by forming joint local councils and electing Arab and Kurdish officials.
But this week, the SDF-held town of Manbij saw protests by Arab residents against compulsory military conscription imposed by the SDF. Hundreds were briefly detained, according to Mohammed Khaled, with activist-operated Aleppo 24.
Ahmed described the protests as "fabricated" by the government and Turkey, which sees Kurdish aspirations as a threat.