The strike on Thursday — by a small, suicide drone — set off a series of retaliatory bombings, and the top US commander for the Middle East, Gen. Erik Kurilla, quickly warned that the US was prepared to launch more attacks if needed.
American troops have been in Syria since 2015, but the latest casualties highlight what has been a consistent, but often quiet, US counterterrorism mission, aimed at countering Iranian-backed militias and preventing the resurgence of the Islamic State group.
A look at the US troop presence in Syria.
IT ALL BEGAN WITH THE ISLAMIC STATE GROUP
On any given day there are at least 900 US forces in Syria, along with an undisclosed number of contractors. US special operations forces also move in and out of the country, but are usually in small teams and are not included in the official count.
They are trying to prevent any comeback by the Islamic State group, which swept through Iraq and Syria in 2014, taking control of large swaths of territory.
For years, the US and its coalition allies battled IS in Iraq and Syria, partnering with the Kurdish-led Syrian Democratic Forces. By 2019, the US declared the Islamic State caliphate destroyed, but remnants of the group remain a threat, including about 10,000 fighters held in detention facilities in Syria and tens of thousands of their family members living in refugee camps.
US forces advise and assist the SDF, including in securing the detention facilities, and they also conduct counterterror missions against the Islamic State group and other al-Qaida-affiliated militants, and carry out strikes on Iran-backed militias that have attacked US facilities.
Russia, an ally of the Syrian government, is also active in the country, but Washington and Moscow have used a deconfliction phone line in an effort to avoid conflict there.
IRAN IS ANOTHER REASON THE US REMAINS IN SYRIA
Tehran’s political influence and militia strength throughout the region have created a security concern for the US Since the defeat of the Islamic State group, Iran-backed fighters have expanded their influence in the region.
The presence of American forces in Syria makes it more difficult for Iran to move weapons into Lebanon, for use by its proxies, including the Lebanese Hezbollah, against Israel.
For example, the al-Tanf garrison in southeastern Syria is located on a vital road that can link Iranian-backed forces from Tehran all the way to southern Lebanon — and Israel’s doorstep. So troops at the US garrison can disrupt what could be an uncontested land bridge for Iran to the eastern Mediterranean.
The oil-rich Deir el-Zour province in eastern Syria, where some of the latest US strikes hit, sits along that strategic route. Syrian government forces and allied Iran-backed groups are deployed on the west bank of the Euphrates River in Deir el-Zour, while American troops support their allies, the SDF, largely along the east bank.
WHAT HAPPENED IN THE LATEST ATTACK?
A small suicide — sometimes called a kamikazi — drone flew low over fencing into the base and struck a maintenance facility where US troops and contractors were working. It did not fire a weapon, but exploded when it hit.
One American contractor was killed, and five US service members and another contractor were wounded. One service member returned to duty and the other wounded taken out of Syria for medical treatment. Contractors often are used to help with maintenance and logistical support.
US officials blame Iran, pointing to remnants of the drone, multiple intelligence threat streams and the fact that the attack was so similar to previous ones by the militants. The officials spoke on condition of anonymity to discuss military operations.
In retaliation, US F-15 fighter jets from al-Udeid Air Base in Qatar struck locations near Deir el-Zour, targeting the Iran-backed militias believed responsible for the attack. The number of reported casualties varied, and the US would not confirm any numbers.
In an apparent response to those US airstrikes, 10 rockets were fired Friday at a US base known as Green Village. No one was injured. Air Force Brig. Gen. Pat Ryder, the Pentagon press secretary, said the rockets were fired by groups affiliated with Iran’s Revolutionary Guard Corps, but he stopped short of blaming Tehran for the US deaths and injuries.
AREN’T US TROOPS PROTECTED?
The US maintains security at all of its bases but steadfastly declines to provide much detail. Reporters traveling in Syria, including from The Associated Press, have frequently seen a range of security measures, ranging from fencing and other barricades to more high-tech radars and other sensors.
Asked about information that one of the radars at the base was not working, Ryder said there was not a total gap in radar capabilities: “There was a complete sight picture in terms of radar.”
But Iranian drones represent a serious — and expanding — threat in Syria. Kurilla told Congress that Tehran is building increasingly sophisticated drones, and now has an arsenal that ranges from small, short-range systems “to long-range one-way attack platforms.”
Iran has also provided drones to Russia for use in its ongoing war in Ukraine.
One of the deadliest flare-ups between the US and Iran-backed groups occurred in December 2019, when US military strikes in Iraq and Syria killed 25 fighters and wounded others from the Iran-backed Kataeb Hezbollah Iraqi militia. The US said the strike was in retaliation for the killing of an American contractor in a rocket attack on an Iraqi military base that it blamed on the group.
In August 2022, the US carried out strikes targeting Iran-backed militias in Deir el-Zour province. The Pentagon said the attacks were meant to send a message to Iran, which the US blamed for a number of drone attacks, including one that targeted the al-Tanf garrison. That base was also hit in January, when three suicide drones struck, wounding two Syrian opposition fighters. The US again said Iran-backed groups were responsible.
Israel has also struck Iranian targets in eastern Syria, although it rarely claims responsibility. In November 2022, airstrikes targeted tanker trucks that crossed from Iraq into eastern Syria. The convoy was reportedly carrying fuel and weapons to militias in Deir el-Zour. The US denied involvement, and an Israeli military official later strongly suggested that Israel was behind the strike.