"With backing from the Syrian and Russian air forces, units of our armed forces recaptured the city of Palmyra, in cooperation with the allies," the military said in a statement.
A Britain-based war monitor, said that, the army and Iranian-backed militia advanced inside Palmyra on Thursday as ISIS withdrew completely, the Syrian Observatory for Human Rights.
ISIS militants retreated to areas in the east, the Observatory reported.
Government forces took control of swathes of Palmyra and conducted combing operations to clear mines on Thursday, it said. During ISIS's first occupation which ended in March, the ultra-hardline jihadist group destroyed some of Palmyra's priceless archaeological heritage and is believed to have razed other parts of the historical ruins since regaining control in December.
ISIS is on the back foot in Syria after losing territory in the north to an alliance of U.S.-backed, Kurdish-led militias, and to Turkey-backed Syrian rebels.The Syrian army is also fighting ISIS in the area east of Aleppo, where it is pushing to reach the Euphrates river, and in the city of Deir al-Zor, where it controls an enclave that is besieged by the terrorist group.