A U.S. air raid against Iranian-backed fighters in southern Syria last week represents a volatile new phase of the conflict that could trigger a wider confrontation between the United States and Iran — and their allies on the ground.
Until last week’s strike, the United States and Iran had managed to steer clear of a direct confrontation in Iraq and Syria, where each has hundreds of military advisors on the ground, embedded with local forces. In Iraq, they share a common enemy in the Islamic State. In Syria, the two sides are waging different wars: U.S. aircraft and special operations forces are pushing to roll back Islamic State militants, while Iran is backing the Syrian regime against opposition forces in a multi-sided civil war.
But as the Islamic State’s grip on territory weakens, the United States and Iran are increasingly at odds as their local partners vie for control of key terrain along the Syria-Iraq border.
In the May 18 airstrike, U.S. F-16s hit a convoy of Iranian-armed Shiite fighters who failed to heed warnings to stay away from a base at al-Tanf, close to the Jordanian and Iraqi borders, which is used by American and British special forces to train local militias fighting the Islamic State. The airstrike marked the first time U.S. forces had targeted Iran’s proxies in Syria. A few days later, the Iranian proxies returned to the area, and U.S. warplanes buzzed them in a clear warning to keep away, the Pentagon said Tuesday.
U.S. military officers played down the incidents, saying the airstrike was merely a matter of safeguarding American special operations forces in the country’s southeast.
“This doesn’t signal any change in strategy,” said a senior U.S. military officer, who spoke on condition of anonymity.
The U.S. strategy, under both President Donald Trump and former President Barack Obama, has concentrated on defeating Islamic State forces on the battlefield and depriving them of territory in Iraq and Syria. With the exception of missile strikes against Syria last month in retaliation for its use of chemical weapons, the Trump administration so far has chosen not to enter into a military confrontation with the Syrian regime of Bashar al-Assad, or its patrons — Iran and Russia.
Having pushed Islamic State back in much of northeastern Syria, U.S. commanders are determined to oust the militants from their last urban bastion in Raqqa. A U.S.-armed and trained force of Kurdish and Arab fighters has begun to encircle Raqqa, and once the city falls, American officers hope to hunt down the Islamic State in eastern Deir Ezzor province and the Euphrates River Valley, where the group still exists in force.
But Iran has grown alarmed over the growing presence of U.S. special operations forces in southern Syria, and the progress of Syrian Kurdish and Arab troops on the battlefield. Iran is keen to secure a corridor linking Tehran and Baghdad to Syria and Lebanon, and Tehran state-run media have claimed the U.S. forces are in the border area to block any supply routes for Iran.
In response, Tehran has deployed thousands of Afghan and Iraqi Shiite fighters, and in recent weeks has sent 3,000 Lebanese Hezbollah troops to the southeastern region between al-Tanf and Deir Ezzor, according to reports from Fars news agency, affiliated with Iran’s Revolutionary Guard Corps.
The Hezbollah troops were sent to the al-Tanf area “to prepare the Syrian army and its allies for thwarting the US plots in the region and establish security at the Palmyra-Baghdad road,” Fars wrote, just hours before the U.S. air raid. They could also serve as a blocking force to keep U.S.-backed fighters from moving north out of al-Tanf.
The escalating tensions between Washington and Tehran in Syria coincided with tougher rhetoric from President Trump directed at Iran. In a speech this week in Saudi Arabia, Trump labeled Iran as a source of “destruction and chaos,” and called on countries in the region to form a united front against Tehran.
Although Trump has promised to adopt an aggressive stance with Tehran, the White House is still conducting a review of its policy toward Iran and the administration has yet to articulate U.S. goals along the Syria-Iraq border.
“It’s not clear to me yet if the administration has a detailed strategy [on] how to manage its presence and its allies’ presence in eastern Syria,” said Robert Ford, former U.S. ambassador to Syria and now a fellow at the Middle East Institute.
“If the administration is not careful, it’s going to be a slippery slope. It seems like there’s a potential for more conflict.”
The Trump administration has given the U.S. military the authority to base about 1,000 troops — mostly special operations forces — in Syria, spread out among several small outposts in the Kurdish north, a Marine Corps fire base close to Raqqa, and at al-Tanf in the south. These small outposts are separated by hundreds of miles of territory where the Islamic State is steadily losing control, and which regime forces and their Iranian allies see as fertile ground to reestablish the Syrian government’s control.
The U.S.-led coalition is keeping a wary eye on the militias. One U.S. defense official told Foreign Policy they are watching the militias inch their way eastward toward Deir Ezzor, where the Syrian government maintains a significant — and isolated — military outpost. The base has long been cut off from other areas of regime control and can only be resupplied by airdrops, but it was recently reinforced by about 1,000 Syrian soldiers, giving the regime in Damascus some fighting power in the area.
American military leaders have long said they expect the Islamic State to retreat into the Euphrates River Valley that connects Raqqa to the Iraqi border, and U.S. and coalition aircraft have been striking ISIS targets in the valley for months. U.S. warplanes carried out more air strikes in the area this week.
Some of the Iranian-backed militia fighters remain in place near al-Tanf, despite the U.S. airstrike and last weekend’s warning. “If they resume their advance, coalition forces will defend themselves,” Pentagon spokesman Capt. Jeff Davis told reporters on Tuesday.
Another military official added that “we have a good understanding they will want to continue moving east” toward Deir Ezzor, and the fighters are being closely tracked.
When the fight moves to the Euphrates valley in Deir Ezzor, the risks of an unintended conflict will grow. With U.S-backed Free Syrian Army forces moving from the south, Kurdish and Arab Syrian Democratic Forces advancing from the north and west, pro-regime militias trying to push into the area and both American and Russian aircraft buzzing overhead, some worry that the crowded battlefield could lead to unwanted incidents.
The Iranian supported militias often operate in close proximity to U.S. troops, especially in Iraq. An FP reporter, visiting a U.S. military base south of Mosul earlier this year, saw a chart in the operations center with the flags of the major armed Shiite militias operating in the vicinity, so U.S. forces could identify what groups are operating close by, often just on the perimeter of their base.
Last September, U.S and coalition jets inadvertently struck a small outpost in the east of Syria, killing over 60 Assad regime soldiers in an incident that angered Moscow and highlighted how confused the battlefield there can be.
With American troops on the ground, and advisors moving around with small local units, there remains the danger of Iranian retaliation. During the U.S. occupation of Iraq, Tehran provided Shiite militias with deadly roadside bombs and rockets that claimed hundreds of American lives.
Already, Iranian-backed Iraqi militia groups have increased their anti-U.S. propaganda in Iraq, accusing Washington of “aiding the Islamic State and pressuring the Baghdad government to ‘expel’ American troops advising the Iraqi security forces in Mosul and across the country,” Ahmad Majidyar, director of the IranObserved Project at the Middle East Institute, wrote recently.
“Any response from Iran would be asymmetrical,” Majidyar said, “and could come in places like Iraq.”
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