“The armed forces, in cooperation with allied forces, liberated the city of Deir al-Zor completely from the clutches of the Daesh terrorist organization,” the military source said, using an Arabic acronym for Islamic State.

The army, backed by Russian bombers, Iran and Shi‘ite militias, is advancing toward the last significant town held by Islamic State in Syria, Albu Kamal, which is also located on the western bank of the Euphrates.

A rival offensive by Kurdish and Arab militias supported by a U.S.-led coalition with air strikes and special forces, is pressing Islamic State on the eastern bank.

Iraqi forces on Friday said they had begun their own final offensive against Islamic State on the Iraqi side of the jihadist territory that straddles the border between the two countries, entering the city of al-Qaim.

Islamic State had for years besieged a government enclave in Deir al-Zor until an army advance relieved it in early September, starting a battle for jihadist-held parts of the city.