The US military has launched strikes on dozens of sites manned by Iran-backed fighters in western Iraq and eastern Syria in retaliation for a drone strike in Jordan in late January that killed three US service members and wounded dozens.

Tensions had been rising since the Israel-Hamas war started on October 7 and a week later Iran-backed fighters, who are loosely allied with Hamas, began carrying out drone and rocket attacks on bases housing US troops in Iraq and Syria. A deadly strike on the desert outpost known as Tower 22 in Jordan near the Syrian border further increased tensions.

The US retaliation had been expected since the January 28 attack in Jordan.

Why is the area that was struck important?
The 85 targets struck in seven locations are in a strategic region where thousands of Iran-backed fighters are deployed to help expand Iran’s influence from Tehran to the Mediterranean coast.

US bases in Syria’s eastern province of Deir el-Zour and the northeastern province of Hassakeh have come under attack for years. The Euphrates River cuts through Syria into Iraq, with US troops and American-backed Kurdish-led fighters on the east bank and Iran-backed fighters and Syrian government forces to the west.

Bases for US troops in Iraq have come under attack too.

Iran-backed militias control the Iraqi side of the border and move freely in and out of Syria, where they man posts with their allies from Lebanon’s powerful Hezbollah and other Shiite armed groups.

An RAF Typhoon aircraft taking off from RAF Akrotiri in Cyprus, for a mission to strike targets in Yemen. The US and British militaries bombed more than a dozen sites used by the Iranian-backed Houthis in Yemen Photo / UK Ministry of Defence via AP

Which targets were hit and how many people were killed?

The US military said that its massive barrage of strikes hit command and control headquarters; intelligence centres; rockets and missiles, drone and ammunition storage sites; and other facilities connected to the militias and the Iranian Revolutionary Guard’s Quds Force, which handles Tehran’s relationship with, and arming of, regional militias.

• Three US troops are killed and dozens are injured in a drone strike by Iran-backed militia in Jordan
• What is Tower 22, the military base that was attacked in Jordan where three US troops were killed?

Syrian opposition activists said the strikes hit the Imam Ali base near the border Syrian town of Boukamal, the Ein Ali base in Quriya, just south of the strategic town of Mayadeen, and a radar center on a mountain near the provincial capital that is also called Deir el-Zour.

Rami Abdurrahman, who heads the Britain-based Syrian Observatory for Human Rights, said 29 rank-and-file fighters were killed in those strikes.

The attacks also hit a border crossing known as Humaydiya, where militia cross back and forth between Iraq and Syria, according to Omar Abu Layla, a Europe-based activist who heads the Deir Ezzor 24 media outlet. He said the strikes also hit an area inside the town of Mayadeen known as “the security quarter.”

Tower 22 in northeastern Jordan. Photo / AP

Iraqi government spokesperson Bassim al-Awadi said the border strikes killed 16 people and caused “significant damage” to homes and private properties.

The Popular Mobilization Force, a coalition of Iran-backed militia that is nominally under the control of the Iraqi military, said the strikes in western Iraq hit a logistical support post, a tanks battalion, an artillery post and a hospital. The PMF said 16 people were killed and 36 wounded, and that authorities were searching for other missing people.

How will Iran-backed fighters retaliate?

Iran and groups it backs in the region aim to put pressure on Washington to force Israel to end its crushing offensive in Gaza, but do not appear to want all-out war. The defeat of Hamas would be a major setback for Tehran, which considers itself and its allies the main defenders of the Palestinian cause.

The Islamic Resistance in Iraq, an umbrella group for Iran-backed groups, said it carried out two explosive drone attacks Saturday on bases housing US troops in the northern Iraqi city of Irbil and a post in northeast Syria near the Iraqi border.

Houthi fighters and tribesmen stage a rally against the US and British strikes on Houthi-run military sites near Yemen. Photo / AP

The only Iran-backed faction that has been escalating are Yemen’s Houthi rebels, which have targeted commercial ships and US warships in the Red Sea with drones and ballistic missiles. The US has carried out strikes against Houthis in Yemen over the past two weeks. There have been no new attacks by the Houthis since the US strikes in Iraq and Syria.