Deir al-Zour – on the west bank of the Euphrates River – had been divided into a government-held and an Isis-held part for nearly three years. Also known as Deir Ezzor, it is the largest city in eastern Syria and the capital of the province with the same name. It is also the largest to be recaptured by the Syrian government from Isis.
The Syrian army, backed by Russia and Iran, and Kurdish-led Syrian forces, backed by the United States, are now racing to take the rest of the oil-rich eastern province of Deir el-Zour, including the key town of Boukamal near the Iraqi border.
Just across the border from Boukamal lies the town of al-Qaim, Islamic State's last territorial stronghold in Iraq. An Iraqi officer in Iraq's western Anbar region said they are pushing into western neighbourhoods of the town. Iraq's Prime Minister Haider al-Abadi pledged the battle will be finished within days.
The strategically located town was used by Isis to ferry fighters and supplies between the two countries at the height of the caliphate, when they held nearly a third of both Iraq and Syria.
The US-led international military coalition, which has run an air campaign against Isis in both Syria and Iraq since 2014, said in a statement that approximately 1,500 jihadists were estimated to remain in the immediate vicinity of al-Qaim.
The militants, routed from one urban stronghold after another, have recently been moving deeper into Syria's remote desert, where experts say they are regrouping and preparing to return to guerrilla-style attacks including scattered hit-and-run and suicide bombings.